the video connection book - panasonic

7/28/2019 The Video Connection Book - Panasonic

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T E C H N O L O G Y


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Systems and their applications are based on theconnection of individual devices. A well-known standard

for connecting digital TV devices is the so-called SDI(Serial Digital Interface) format, which was defined morethan a decade ago to carry the uncompressed digitalcomponent signal.

Together with the introduction of video compressionformats, new methods for the transport of these newcompressed video signals were defined, methods whichare based on the introduction of a Serial Data Transport

Interface (SDTI). This SDTI signal forms a bridge to thedata transport technologies of the computer and telecomindustries.

The Video Connection Book was not written fordevelopment or planning engineers, but for editors,directors and broadcast managers. To provide basicinformation about connection techniques theirdifferences and applications we have had to drastically

simplify technical facts. Engineers should study the relevantStandards of SMPTE and other organizations for moreinformation.

3VideoConnection

Introduction


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Chapter 1 Page 6

The TV Legacy and Modern Telecommunication Philosophy

The Principle of Layering in TelecommunicationStandards

Chapter 2 Page 8

Steps from Analog to Digital Video

Chapter 3 Page 12

The Serial Digital Interface andCompressed Video Signals

Cascading of Compression Codecs

Chapter 4 Page 15

The Need for a Truly Data Signal

Chapter 5 Page 18

Differences between the Video-Centric World of SDIand the Data World

Chapter 6 Page 21

Audio Signals within the SDI Bit-Stream

Chapter 7 Page 23

From SDI to SDTIThe Serial Data Transport Interface

Chapter 8 Page 27

The Meaning of Interoperability for Broadcast Facilities

Chapter 9 Page 29

The Meaning of Network Technology for BroadcastFacilities

Chapter 10 Page 31

DVCPRO, the DIF Packet and the World of Data Signals

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C O N T E N T S

VideoConnection

Chapter 11 Page 33

The Transport of DVCPRO DIF Packets over SDTI

Chapter 12 Page 38

The Transport of MPEG-2 over SDTI

Chapter 13 Page 42The Stream Transfers of Data

Chapter 14 Page 44

The File Transfers of Data

Chapter 15 Page 47

Fiber Channel

Chapter 16 Page 52

The ATM Wide Area Network

Chapter 17 Page 58

IEEE 1394 More than just a Network for theConsumer Market

Chapter 18 Page 63

The Universal File Exchange Format

Chapter 19 Page 68

Conclusion

References Page 70

Index Page 72

Contacts Page 74


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The big achievement of the color encoding standards,NTSC and PAL, was not only to stay within a giventransmitter bandwidth, but also to reduce a 3 cableinterconnection to a single cable interconnection. Ittherefore became possible at the time of switching fromblack & white to color TV to use the same coaxial cables

for color, as were already being used to carry black &white monochrome signals. This was of huge economicbenefit for broadcasters.

The legacy NTSC and PAL formats were defined inso-called vertical standards. Today, telecommunicationsstandards are written in a layered structure. The Societyof Motion Picture and Television Engineers wiselyadopted this principle for structuring its TV standardsas well. The reason for this was the convergence ofthe broadcast and communication industries. Theunderstanding of layers is crucial to the understanding oftodays connection techniques. Figure 1 interprets theanalog color TV standards as a set of layers.

We can differentiate three layers:

Top Layer: The imager CCD is the source for theprimary color signals, which are needed for the display ofimaged information at the receiver. The Top Layer

specifies these parameters.Middle Layer(s): These layers specify the color encodingscheme and the formatting of the color and luminance

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The TV Legacy and Modern Telecommunication Philosophy

The Principle of Layering in Telecommunication Standards


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Connection

C H A P T E R 1

signal into one single CCVS signal. Other parts of thesemiddle layers can define the rules for transporting theCCVS signal over the modulation system of a transmitter.

Bottom Layer: It specifies all physical (electrical &mechanical) parameters level, cable, impedance,connector and is called the Physical Layer.

7

R (red signal)G (green signal)B (blue signal)

Middle Layer

RGB

525/59,94525/59.94 625/50625/50

NTSC PAL-M PAL SECAM

Level: 1 volt ppCable: coaxial

Impedance: 75 ohmsConnector: BNC

Top Layer

Bottom Layer

Modern standards for telecommunicationsare written in a layered structure. Applications are

defined in the top layers, physical interconnection cablesin the bottom layer. Middle layers define rules for transportingthe information and for communication between the involved

hardware & software devices. To ease the convergencebetween broadcast technologies and modern IT &telecom technologies, SMPTE adopted the principle

of layering for its standardization work.

S UMMAR Y

Fig. 1:The legacy color TVstandard shown in amodern layeredstructure


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Over the last few decades, technological progress haschanged the way video information is transported and/orstored. Two decades ago, the 1/2 inch recording industrymoved from NTSC and PAL composite signals to analogcomponent signals. These changes affected the middlelayers, as can be seen in Figure 2. The bottom layer with

the 75 ohm coaxial cable stayed the same.

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R-G-B- Imager525

Middle Layer(s)

Computation of Y, CR andCBanalog component signals

Coaxial cable (3)Impedance: 75 ohms

Connector: BNC

Top Layer

Bottom Layer

R-G-B- Imager625

1/2" analog Camcorder

Fig. 2:Layering model

for analogcomponent signals

Steps from Analog to Digital Video


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In the mid-eighties the first digital D1 VTRs wereintroduced. In order to record TV on these digitalrecorders the analog component signals were digitized.

Another layer, which specified the digitization of theanalog component signals, was added to the middlelayer. The physical bottom layer changed as well. The

digitalized analog signal needed 11 twisted pair wires tocarry the signal (Figure 3).

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C H A P T E R 2

VideoConnection

R-G-B- Imager525

Middle Layer(s)Computation of Y, CR,CBanalog component signals

11 balanced signal pairs carrying clock and 10 data bitsCables: twisted pair (11x)

Receiver impedance: 110 ohmsConnector: 25 contact D subminiature

Top Layer

Bottom Layer

R-G-B- Imager625

D1 Digital VTRs

Digitalization into a parallel digital signal

Fig. 3:Layering model forthe parallel form ofdigital componentsignals


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The parallel digital signal was very awkward to handle.It was no longer possible to use the installed coaxialvideo cables because this signal required a special cable.Due to the use of 10 wire pairs to carry 10 bits, thecable became very thick. The connectors were largeand the distances that could be bridged were too short.

All these problems were solved with the invention of theSerial Digital Signal (SDI), which carried the individual bitsin a serial form instead of a parallel form (Figure 4).

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R-G-B- Imager525

Middle Layer(s)

Computation of Y, CR andCBanalog component signals

Cables: coaxial

Impedance: 75 ohmsConnector: BNC

Top Layer

Bottom Layer

R-G-B- Imager625

Digitalizationinto a parallel digital signal (10 bits = 10 wire pairs)

Serializationinto 1 single serial digital signal (1 bit = 1 wire pair)

Fig. 4:Layering model

for the Serial DigitalSignal (SDI)


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The middle layer now consists of three sub-layers.Comparing Figure 4 with Figure 1 we can see that the topand bottom layers remained unchanged. Only themiddle layer was replaced on the way from analog todigital (Figure 5). This highlights the fact that the SDIsignal can be carried over the same coaxial cable as the

analog color TV signal.

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C H A P T E R 2

VideoConnection

NTSC PAL-M PAL SECAM

Computationof analog component signal

Digitalizationinto a parallel digital signal

Serialization

into 1 single serial digital signal

Fig. 5:Replacement ofthe middle layer onthe way fromanalog to digital

The breakthrough to digital TV facilities was madepossible by using the same Physical Layer of the legacy

analog TV standard.

S UMMAR Y


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Over the last decade, the majority of broadcast facilitieshave moved from analog to digital. Digital Technology hasenabled a variety of new production tools, from digitalvideo effects (DVE) to non-linear editing (NLE).Connections within these digital TV studios as shownin Figure 6 make use of the Serial Digital Signal (SDI),

which is standardized as ANSI/SMPTE 259M. The successof the SDI technique was based on the fact that thissignal could be carried over already installed cables,

which were already being used to carry analog NTSC orPAL signals.

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The Serial Digital Interface and Compressed Video Signals

Cascading of Compression Codecs

SDI - Routing Control

Archiving

AcquisitionProduction

VTRsServers

Playout

Contribution

Post-Production

SDI-RoutingSystem

SDI

Fig.6:SDI the backboneof todays digital TVbroadcast facilities


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In todays daily production processes it has becomeunavoidable to interconnect devices that are internally

based on a compression format. This could be done asshown in Figure 8 via SDI, but would lead to a cascadingof compression codecs.

When SDI was introduced, compression technology wasstill in the laboratories. Therefore it was designed totransport uncompressed video signals only. The VideoCompression Book1) deals with the various newcompression formats and their applications. It explains thatboth DV compression (as used in DVCPRO) andMPEG-2 compression are based on a quantization of theso-called DCT coefficients. This quantization is the mainsource of some unavoidable quality losses in DCTbased compression codecs (Figure 7).

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C H A P T E R 3

VideoConnection

Fig. 7: Compression - Codec = Compression - Encoder + Compression - Decoder

OUT

SDI SDI

RasterTransformation

Quantization VLC

video

DCT

Encoder

Codec = Encoder + Decoder

IN

Sources of Quality Losses in DCT Based Compression Codecs

Decoder

Raster Re-Transformation

DCT

video

VLC Q-1 -1

1) The Video Compression Book was issued by Panasonic in 1999and can be downloaded from Panasonics web page athttp:// www.panasonic-broadcast.com (available in English, Spanish and German).


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Cascading of compression codecs slightly impactspicture quality because the quantization of the DCTcoefficients is repeated several times. Slightly means thatthe difference may not become visible. However, if youcopy a tape via SDI, you dont get a clone of theoriginal. With uncompressed signals, you do! Figure 9

shows the difference in performance of uncompressedand compressed video signals.

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OUT

SDI SDI

IN

DVCPRO device # 1

IN

DVCPRO

RasterTransfor-mation

QuantizationVLC

video

DCT

Encoder

video

DCT Raster Re-Trans-

formationVLC Q-1

-1

Decoder


QuantizationVLC

video

DCT

Encoder

Fig.8:Cascading of

compression codecsvia SDI connections

SDI connections represent the backbone of todaysdigital broadcast facilities. Using these connections for

individual devices that internally apply compressiontechnology may slightly impact the picture

quality.

S UMMAR Y

Fig. 9:Schematic trajectoryof the Signal toNoise Ratio over thenumber of cascadedcompression codecs

S/N

Number of codecs cascaded via SDI2 3

(D1, D5)

DCT compression


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To avoid the possible negative impacts on picture

quality through connecting compression devices via SDI,a new type of connection method was required. Itneeded to be based on a truly data signal.

But what does truly data mean? Is there a differencebetween a data signal and the digital TV (SDI) signal? Toanswer this question, it seems appropriate to make adetour into the world of modern telecommunications.

All communications between devices require that thedevices agree on the format of the data. The set of rules

defining a format is called a protocol. Ethernet is sucha protocol for local-area network (LAN) applications. ANetwork is any collection of independent computers thatcommunicate with one another over a shared networkmedium. LANs are networks usually confined to ageographic area, such as a single building. Ethernet is themost popular physical layer LAN technology in usetoday.

The heart of the Ethernet system is the Ethernet frame,

which is used to deliver data between computers. Theframe is like a packet of variable size, consisting of apacket and an address label.

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C H A P T E R 4

VideoConnection

The Need for a Truly Data Signal

OUTOUT

SDI SDI

IN

DVCPRO device # 3device # 2


QuantizationVLC

video

DCT

Encoder

video


formationVLC Q-1

-1

Decoder

video


formationVLC Q-1

-1

Decoder


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Ethernet frames are bit-oriented frames that contain

Preamble 64 bits (alternating 1s and 0s) used forsynchronization,

Destination address 48 bits,

Source address 48 bits,

Length / Type 16 bits (identifies the amount & typeof payload data),

Payload data 46 to 1500 bytes, and

CRC 32 bits Cyclical Redundancy Check, used forerror detection.

Ethernet describes the physical layer of a network. TCP/IPis the most commonly-used set of transport layers abovethat physical layer. The Transmission Control Protocol(TCP) and the Internet Protocol provide the basic transportfunctionality.

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LabelPayload

Preamble

8 Bytes

AddressDestination Source

6 Bytes 6 Bytes

Length/Type

2 Bytes4 Bytes46 - 1500 Bytes

CRCData

Label

Paylo

adFig. 10:

The Ethernetpacket consistingof a packet andan address label


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TCP/IP breaks your information up into a sequence ofsmaller datagrams. A datagram is a collection of data thatis sent as a single message. Each of these datagrams is sentthrough the network individually to the other end, wherethey are re-assembled. However, while datagrams are intransit, the network doesnt know there is any connectionbetween them. It is perfectly possible that datagram 14

will actually arrive before datagram 13. It is also possiblethat somewhere in the network, an error will occur, andsome datagram wont get through at all. In that case, it hasto be sent again. In the context of this book a datagramis no different from a packet plus label (IP Header).

The Transmission Control Protocol is responsible forbreaking up the message into datagrams, addressing thehost, reassembling the datagrams at the other end,resending anything that gets lost, and putting things

back in the right order. The Internet Protocol isresponsible for routing individual datagrams.

On top of TCP/IP is the so called File TransferProtocol (FTP), which provides the necessary commandset to transport data files from one computer to another.

We have seen that a data signal is characterized bypackaged data. Each package has its label to identifysource, destination and type of payload.

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C H A P T E R 4

VideoConnection

The packaging of data described above, forms the

so-called truly data signal. It means the combination of apayload of data with a label or header that provides additionalinformation about the payload type, size, source and

destination.

S UMMAR Y


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The SDI signal is only the digital representation of theanalog Y, CR and CB video signals. During the analog todigital conversion process the video signals are sampledinto 720 luminance pixels and 720 chrominance pixels(360 for CR, and 360 for CB) per line. Each pixel isassigned 10 bits. In the sequence shown in Figure 11, the

serial SDI signal carries the bits of the samples of oneactive TV line.

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Differences between the Video-Centric World of SDI and theData World

Fig. 11:Bit sequence within

the SDI signal for aone line period Horizontal blanking

TV-line n TV-line n+1 TV-line n+2 TV-line n+3 TV-line n+4

Gr. 359 Gr. 360

40 bitsEAV40 bits 40 bits

Group 2 Group 3

40 bits 40 bits10 bits10 bits10 bits10 bits

Group 1

40 bitsSAV

CB CR YY


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The horizontal synchronization information of the analogvideo signal is translated into two special markers of 40bits each. The Start of Active Video (SAV) signal precedesthe first group of each line and the End of Active Video(EAV) follows the last group. These signals do notrepresent a label, because they provide no information

about source, destination, and length or type of payloade.g. the number of TV-lines. Additional informationembedded in the EAV and SAV signals indicates verticalblanking and the field sequence.

The transmitted payload of 14,400 bits per active line canonly be interpreted correctly when the receiver hassynchronized itself to the incoming SDI signal with thehelp of the digital horizontal synchronization signalsEAV and SAV. The receiver then counts the SAV signalsand assigns the correct line number to the payload. In the

worst case, the synchronization time may be as longas one field of video. All payloads received during thistime may be lost. In the data world a label attached to thepayload will avoid such a loss.

The above-described SDI version is based on a samplingfrequency of 13.5 MHz for the luminance video signal.There is another version with 18 MHz sampling forluminance. That version carries 19,200 bits as payload peractive line. Figure 12 shows the basic structure of the SDIsignal for the period of one line.

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C H A P T E R 5

VideoConnection


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Packetized communication can be synchronous orasynchronous. Synchronous signals are closely tied tosome sort of clock, so each packet begins, for example,precisely at 0.0 ms, then 7.5 ms, then 15.0 ms, and so on.Asynchronous signals are not bound tightly to a clock.Their data packets usually have some kind of unique bit

pattern to identify the beginning and end of a packet.Most serial communications and practically all LANcommunications are asynchronous. Synchronizationbetween transmitting and receiving devices can beachieved through the transport of timing references

within the stream. An additional prerequisite for asynchronous transmission of a TV signal via anasynchronous line is the availability of so-calledQuality of Service parameters as explained later.

The connection of two devices over SDI provides atransmission that is not only synchronous, but real-timeas well. A synchronous data communication can beeither real-time or non-real-time.

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The SDI signal is a digital representation of analogvideo signals, but it is not a data signal. The video data arenot packaged and no label identifies the content, its

source or its destination.

S UMMAR Y

Ancillary Data Payload14,400 bits at 270 Mb/sec19,200 bits at 360 Mb/sec

EAV

SAV

Fig. 12:Basic structureof the SDI signal forone line period.


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Not all bit space within the SDI signal is occupied byvideo. Figure 13 shows that the space available betweenthe EAV and the SAV signals, which equals the horizontalblanking period of analog video, can be used to carrydigital audio signals.

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C H A P T E R 6

VideoConnection

Audio Signals within the SDI Bit-Stream

Active Video

of Field 1

EAV

SAV

Optional video data

Active Video

of Field 2

Optional video data

Audio

Audio

H

V

Fig. 13:Available spacewithin SDI for a

period of one TVframe which can beused for embeddingaudio into the SDIbit-stream


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The ID-bits identify the payload as audio samples and thelength specifies the variable number of audio samples inthe packet as shown in Fig.14. The checksum (CS) is used

to determine the validity of the data packet. The packetsare placed in the space indicated in Figure 13. The samepacket structure is used to transport the AES auxiliary dataor any other type of data. The ID is used to identify thetype of data in the payload.

Although the video data are not packaged (as explainedabove), the packaging of the digital audio signal becamemandatory due to two reasons:

not all lines are available to carry audio, and

the audio sampling frequencies lead to a non-uniformdistribution of audio samples over the available lines. As

an example, some television lines may carry threesamples, and some four. Other values are also possible.

The AES 3 digital audio stream contains in addition tothe digital audio samples AES auxiliary data and someaudio data that are related to each audio sample. Theaudio samples and the audio data are packed (mapped)into a so-called Ancillary Data Packet.

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Label

Flag

30 bits

ID Length

20 bits 10 bits

Payload

30 bits

Sample

30 bits

Sample

30 bits

Sample

------- 10 bits

CS

While the video part of the SDI signal does not representa truly data signal, the audio signal is embedded within the

SDI signal in the form of packetized data using a labeledpayload.

S UMMAR Y

Fig. 14:Data Packetcontaining theaudio samples of theAES 3 audio stream


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The embedded audio shows that the SDI signal can beused as a type of container for packetized data. You maycompare it with a truck carrying a container as shown inFigure 15. The truck has two freight compartments, asmall one in the front of the truck (usually used as acabin for the driver) and the huge container.

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C H A P T E R 7

VideoConnection

EAV

SAV

Ancillary data PayloadFig. 15:The SDI signal

as container forthe transport ofpacketized data

From SDI to SDTI

The Serial Data Transport Interface


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The Serial Data Transport Interface (SDTI)

places Header Data into the Ancillary Data space,

places User Data into the Payload, and

adds CRC to the User Data.

Using our example you may say that the freight papers areplaced in the small forward compartment with the freightload placed in the container on the trailer.

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EAV

SAV

Ancillary Data Payload

HeaderData

User DataCRC

Header

User DataCRC

Fig. 16:Basic structure ofthe Serial DataTransport Interface(SDTI) signal


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The Header Data is packed into an Ancillary Data Packetshown in Figure 17. The packet structure is identical tothe structure used for embedding audio into the SDIsignal as explained in chapter 6.

The Header Data contain such information as

Line number,

Length of the SDI payload,

Destination address,

Source address, and

Identification for Fixed Block Size or Variable BlockSize within SDI payload.

The Header Data contain the information of a label,which belongs to the User Data in the payload section of

the container. We placed these label data in the payloadof a packet (Figure 17). Then this packet of Header Datagot its own (different) label.

User Data organization and their location within thepayload are not defined by the SDTI standard. This is donein separate application documents for different types ofpayloads.

The payload is structured in Data Blocks. They can be offixed block size or variable block size. Each 10 bits of a data

block can carry either 8 bits or 9 bits of User Data.Figure 18A shows the structure for a Data Block of fixed sizeand Figure 18B the same for a Data Block of variable size.

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C H A P T E R 7

VideoConnection

Fig. 17:Header Data inthe Serial DataTransport Interface(SDTI) signal

Label

Flag

30 bits

ID Length

20 bits 10 bits

Payload

460 bits

Header Data

10 bits

CS


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A data block header precedes each data block. The datastructure for the data block header is shown in Figure 18.The header contains the following information:

Type identifies the type of data stream (for exampleDVCPRO), and

Word Count provides information about the length

of the variable sized Data Block

With the variable block size, consecutive block datawords can be of any size. The next data packet caneither be placed immediately after the previous one, oron the next line. A Separator and End Code support thecorrect word synchronization.

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Fig. 18:(A) SDTI payloadstructure for DataBlocks of fixed size

(B) SDTI payloadstructure for DataBlocks of variable

size

Data Block End Code Word CountTypeSeparator

Header

Data BlockType

Header

The SDI signal is used as a container forpacketized data signals. This SDI container has

two compartments. The first one (the former horizontalblanking area) is used to carry a Data Header that is in no waydifferent to the usual label explained in chapter 4. The second,larger compartment (the former area for the active line part of

the video signal) is used to carry the actual (User) Data.Specifications for the organization of this payload

(e.g. DVCPRO) are defined in separateapplication documents.

S UMMAR Y


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The European Broadcasting Union (EBU), the largestUser Group worldwide, is concerned about theinteroperability of equipment from different vendors. Inthe year 2000, EBU experts analyzed the situation andreported that they had found

different signal types (DV, DV-based & lots of

MPEG-2 interpretations), different interfaces which can be used to transfer

those signals,

different file formats to transfer content as files,

different streaming format to transfer in real-time andfaster, and

consequently: too many possibilities to transfer signals.

The EBU experts suggested the following steps as apath to a solution:

limit the number of different options,

agree to use common transfer mechanisms, andcontainer and file formats for DV, DV-based andMPEG-2 content, and

come to a common understanding for the terminteroperability in the TV and IT worlds.

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C H A P T E R 8

VideoConnection

The Meaning of Interoperability for Broadcast Facilities


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Along this proposed path the EBU experts definedlevels of interoperability:

Level 0: the ability to exchange data,

Level 1: the ability to understand and process these data,and

Level 2: reliable and maintained content quality

throughout the TV production chain, which requires, forexample, that different MPEG-2 encoder and decoderimplementations achieve the same quality

The European Broadcasting Union summarized itsopinion in the official EBU Statement D89 as follows:

The EBU is of the opinion, that interoperability

is achieved if the essence (audio, video) generated at the source

passes through the production process withoutimpairment,

metadata passes through the system without error,

the components used to build a system can beinterconnected by a simple plugging operation,

the interconnection of system components isindependent of manufacturer, and

when required, real-time transfer faster than real-timecan be achieved.

Well-defined and standardized interconnections betweenindividual devices are one of several necessary means tofulfill these requests and to make devices and theirapplications interoperable.

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Networks are the collection of elements that process,manage, transport, and store information, enabling theconnection and integration of multiple computing,control, monitoring, and communication devices withinone local facility (Local-Area Networks = LAN); or evenbetween locally separated facilities (Wide-Area Networks

= WAN).The main reasons why all hardware and softwaredevices within a broadcast facility should be networkedare:

to share resources (storage devices, productionequipment, NLE-systems, DVE-units, archives), and

to share content (audio, video, data, metadata) amongusers.

The implementation of network technology isexpected to increase productivity.

EBU experts reported that they are expecting:

to get the functionality to exchange information inreal-time, faster than real-time but also slower thanreal-time (faster or slower than the captured event),

extended use of file transfer,

to give a higher number of users access to information,

to apply the so-called client/server-technology to givemore than one user access to the same resource at thesame time,

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C H A P T E R 9

VideoConnection

The Meaning of Network Technology for Broadcast Facilities


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to get enhanced connection topologies (not only point topoint),

to transfer different signal types over one commontransport medium, and

to avoid picture quality degradation just for thepurpose of the transmission.

The following characteristics are used to categorizedifferent types of networks:

Topology: The geometric arrangement of a networksystem. Common are bus, star, and ring topologies.

Protocol: The protocol defines a common set of rulesand signals that are used by devices on the network tocommunicate. One of the most popular protocols forLANs is Ethernet (explained in chapter 4).

Computers on a network are sometimes called nodes, orprocessing locations. Every node has its own uniquenetwork address. Computers and devices that allocateresources for a network are called servers.

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Video network technology is expected toprovide broadcast facilities with the tools to increase the

efficiency of their business processes. This will mainly be

achieved by giving a higher number of users access toinformation and resources, and through giving more thanone user access to the same resource at the same

time.

S UMMAR Y


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It was explained that SDI is only a digital representationof an analog TV signal. Features of a data signal are thepacket and the label. Although digital VTRs DVCPROfor example communicate quite well via the establishedSDI signal, internally they already apply the technique ofpackaging and labeling. DVCPRO uses quite a special

package, the so-called DIF package. DIF means DigitalInterface. The DIF package (sometimes called DIF-blockas well) has its origin within the tracks of a DVCPROrecording as shown in Figure 19.

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C H A P T E R 1 0

VideoConnection

DVCPRO, the DIF Packet and the World of Data Signals

DVCPRO tape33.8 mm/s

12 tracks/frameDIF packet

ID (label)

data

C U E T R A C K

C T L T R A C K

18m

6.35 mm

Fig. 19:Digital Interface(DIF) packets in themagnetic tracks of aDVCPRO recording


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Each magnetic track (Figure 19) contains 135 DIF blocksof video data, 9 DIF blocks of audio data, 3 DIF blocksof video auxiliary data and an additional 16 DIF blocks,

which carry error protection data for video and audio. Atthe digital interface video and audio blocks are mixed intothe video & audio section of 144 DIF blocks. A DIFsequence is completed with additional 6 DIF blocks,

which carry, for example, information about videoauxiliary data (VAUX) and time code. In 525/60, a videoframe is composed of 10 such DIF sequences.

Each DIF block consists of a 3-byte ID and 77 bytes of dataas shown in Figure 20.

The ID identifies the type of data in a DIF block andprovides a block number.

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Fig. 20:

Digital Interface(DIF) packet as usedin DVCPRO

DIF-Data

(Byte #0..#2)

0 1 2

(Byte #3... #79)

DIF-ID

3 4 5 6 7 8 9 77 78 79

DVCPRO is well prepared for the data world. Italready records data packages called DIF packets. Due to

the nature of these DIF packets they can be easily placed intoan SDTI container, as explained in chapter 7. They can be

picked out of the SDTI container and re-recorded onDVCPRO without any loss of quality.

S UMMAR Y


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SDI as explained in chapter 7 can be considered asa container and underlying transport for data. SDTIprovided the general rules as to how to load User Datainto this container. SDTI does not specify exactly how theDVCPRO DIF packets should be placed within thecontainer. This is done by a specific protocol (SMPTE

321M).The first step is to re-package the DIF packets.Telecommunications people call this Mapping. [Theymust like this procedure very much, because they useit intensively.] Re-packaging can mean:

placing several smaller packets into one larger box,and attaching a new label to the box, thus creating anew larger packet, or

distributing the contents of a large packet into a

number of smaller packets. This procedure requiresthat each of the new smaller packets be given aunique number and that an algorithm be added so thatthe receiver of the smaller packets can re-combine theoriginal contents of the large packet.

So-called containers are used to transport data packages.These containers may fit the size of the packages or theymay be too small or too large. If they are too small, youhave to start a re-packaging procedure, similar to the one

described above. If the container can carry more than onepackage, it can carry different types of packages. Thefreight papers, i.e. the label, must contain sufficient

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C H A P T E R 1 1

VideoConnection

The Transport of DVCPRO DIF Packets over SDTI


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A specific ID called SDTI Type provides informationabout the use of fixed size SDTI blocks. The SDTI formatsupports blocks of fixed or variable size as payload in thecontainer. DVCPRO uses a version with a fixed sized blockas shown in Figure 21B. This block contains two originalDIF packages as shown in Figure 21A.

information to identify each individual package. To simplifythings, you can imagine the container as just a new type ofpackage, which can carry several other packages.

Lets return to our DIF package (DIF Block). Its structureand size were explained in chapter 10. Figure 21 showshow two DIF blocks are combined into one fixed size SDTI

block.

34

EAV

SAV

Ancillary Data Payload

1,440 words at 270 Mb/s

1,920 words at 360 Mb/s

HeaderData Space

SpaceType

DIF-Data

DIF-Data

Type

DIF-Data

DIF-Data

Type

DIF-Data

DIF-Data

Type

DIF-Data

DIF-Data

SDTI-Type

1word

SignalType

6words

DIF-ID

3words

DIF-Data

77words

DIF-ID

3words

DIF-Data

77words

CRC

4words

SDTI block of fixed size with 170 words

C

B

DIF-ID

3 bytes

DIF-Data

77 bytes

DIF blockA

Fig. 21:

DIF Block (A).

SDTI block of fixedsize with 170 wordscarrying 2 DIF

blocks (B

).

SDTI containercarrying SDTI blockswith DVCPRO DIF

packets (C).


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A specific label Signal Type provides information such as:

the specific type of video frame (number of lines,interlaced/progressive, field/frame frequency),

the DIF structure format (DVCPRO or DVCPRO 50), and

the transmission rate flag (normal, 2 times, 4 times).

Figure 21C shows how the SDTI container is filled withSDTI blocks.

An SDTI data block of the fixed-block variety (as used byDVCPRO) includes two DIF blocks and associated words.In the 525/60 system, the compressed video data stream

within an SDI video frame is composed of 750 SDTI datablocks (1500 DIF blocks) for the 25 Mb/s compressionstructure, or 1500 SDTI data blocks (3000 DIF blocks) forthe 50 Mb/s structure. The figures for the 625/50system are 20% higher.

The data rate of an SDI connection (= physical layer) usedfor SDTI, equals 270 or 360 Mb/s. This bandwidth iscompletely used when carrying uncompressed video, butonly part of it is used when transporting one singlecompressed video signal as provided by DVCPRO. Thespace occupied by one DVCPRO signal is called aChannel Unit. Up to four DVCPRO signals can be carriedthrough one 270 Mb/s SDTI pipe as shown in Figure 22.

35

C H A P T E R 1 1

VideoConnection

1 DVCPRO signal

270 Mb/s pipe

4 DVCPRO signals

270 Mb/s pipe

36 Mb/s 36 Mb/s

36 Mb/s

36 Mb/s

36 Mb/s

Fig. 22:

The availablebandwidth of a 270Mb/s SDTI pipe canbe used to carry upto 4 DVCPRO signals


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A channel unit is a series of SDI raster lines into which SDTIdata blocks are mapped. Each channel unit can carry anindividual DVCPRO compressed video signal. In the caseof 25 Mb/s DVCPRO a channel unit is composed of theSDTI data blocks of one compressed video frame andoccupies the space of 94 SDI raster lines, as shown inFigure 23. One SDI video frame can contain up to4 channel units with the 270 Mb/s interface (Figure 22) or6 channel units with the 360 Mb/s interface.

36

EAV

SAV

94 lines - Channel Unit 0

H

Line 21

Line 525




V

HEADE

R

HEADER

Fig. 23:Series of raster linesin one SDTI frame

forming ChannelUnits occupied byindividual DVCPROsignals


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DVCPRO 50 uses the space of two adjacent channel units.

A 25 Mb/s DVCPRO signal, which should be transportedat four times the normal speed, uses the space of all4-channel units available with the 270 Mb/s interface.

A 50 Mb/s DVCPRO 50 signal, which should betransported at twice the normal speed, also uses the

space of all 4-channel units.

37

C H A P T E R 1

VideoConnection

C H A P T E R 1 1

SDTI

On-Air ServerSDTI

SDTI

SDTI

DVCPRO ServerSDTI4x

SDTI4x

SDTI

Preview

Switcher

SDIRouter

SDIRouter

4x

Fast TransferArchive

4X VTR

DVCPRONon-Linear

Editor

DVCPRO uses only about one quarter of thebandwidth supported by SDTI. This enables up to four

different DVCPRO compressed video signals to be carriedover one SDTI cable or a video clip to be transported at 4times the normal speed from a Camcorder VTR into

an NLE editing server.

S UMMAR Y

Fig. 24:DVCPRO 4X

Transfer System


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The Video Compression Book explained in detail thedifferences between DV compression and MPEG-2compression. DV compression as used by DVCPRO results in a fixed number of bytes per frame (Figure 25 c)

where as MPEG-2 can result in a variable number ofbytes per frame (Figure 25 b).

These differences are reflected in the procedure that is usedto map the compressed video into the SDTI structure. Theprevious chapter explained that the DVCPRO signal ismapped into SDTI blocks of a fixed predetermined size. The

25 Mb/s DVCPRO signal always occupies a fixed,predetermined number of 94 lines within the raster lines ofthe underlying SDI transport. This procedure cant be applied

38

The Transport of MPEG-2 over SDTI

a

b

c

B I B P B I

Bytes

Bytes

Frame-type

Frame

Time

Fig. 25:Number of bytes/

frame for MPEG-2(b) and DVCPRO (c)

types of compression


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to an MPEG-2 signal whose byte count per frame varies asshown in Figure 25.

SDTI does not specify how DVCPRO or MPEG-2 data areplaced within the container provided by SDTI. This is doneby specific protocols. DVCPRO uses a protocol defined inSMPTE 321M. Due to its inherent differences, MPEG-2 uses

a completely different protocol, called SDTI-CP, which isdefined in SMPTE 326M.

CP means Content Packages. SDTI-CP is a packagingstructure for the assembly of:

a system item that carries control information andany metadata which is related to the picture, audio andauxiliary data items,

a picture item,

an audio item, and

an auxiliary item, which carries ancillary data lines,teletext, or other data.

Figure 26 shows the basic structure of a ContentPackage. It is constructed of the four items listed above.

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C H A P T E R 1 2

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Content Package

ITEMS

AudioAuxiliary

SystemPicture

Fig. 26:Basic structure of aContent Package


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The filling of the payload column shown in Figure 27varies over time due to the variable amount of bytes per

frame, which is typical for an MPEG-2 compression. Thisvariation is shown in Figure 28 over a 12-frame MPEG-2GOP sequence.

The system, picture, audio and auxiliary items are eachformatted as SDTI variable blocks. The data structure of avariable length block was shown in Figure 18 of chapter 7.The data in each SDTI variable block continue through asmany lines as necessary.

40

EAV

SAV

Picture item

H

V

1st field

2nd field

Audio item

Auxiliary item

HEADER

System

itemLine 13

Line 525

CRC

Fig. 27:Series of raster linesin one SDTI frame

for a ContentPackage consistingof system, picture,audio and auxiliaryitems.


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On one hand, SDTI-CP offers an extremely flexiblemeans of transferring content over SDTI, while on theother, it demands unnecessarily complex receivers/decoders if all possibilities are to be met. To limit theserequirements in order to allow practical working devices,

decoder templates for the encoding of SDTI-CP withMPEG coded picture streams were defined (SMPTE RP204). This situation with MPEG is well known.Theoretically, it also offers extreme flexibility, which inpractice leads to very complex problems. Therefore, theso-called flexibility of MPEG-2 was first restricted byoperating ranges (forthcoming SMPTE RecommendedPractice 213) and finally by one single specificimplementation (forthcoming SMPTE Standard 356M).

41

C H A P T E R 1 2

VideoConnection

Differences between DV- and MPEG-2compression are reflected in the procedure that is

used to map compressed video into the SDTI structure.MPEG-2 video is part of a Content Package, which carries a

system, picture, audio and auxiliary data item. MPEG-2compression leads to a variable number of bytes per frame,which results in variable sizes of the Content Packages.

On the contrary, DVCPRO signals provide a constant bytestream per frame. The application of SDTI forMPEG-2 signals is therefore much more

complex than for DVCPRO signals.

S UMMAR Y

I

1st field

2nd field

B B P B B P B B P B B

Fig. 28:Variable fillingof the raster lines ofone SDTI frame witha Content Packagecarrying an MPEG-2

video item shownover a 12-frameGOP sequence.


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A Stream is a collection of data sent over a data channelin a sequential fashion as a continuous flow of data(video, audio, etc.). The bytes are typically sent in smallpackets, which are reassembled into a contiguousstream. In the context of TV broadcast, streaming oftelevision program material involves the following

characteristics: a continuous process in which the transmitter pushes

program material to receivers that may join or leave thestream at any time;

the receiver may need some time to synchronizeitself to the streamed signal, e.g. in TVapplications the receiver needs to wait at leastuntil the start of the next frame,

there is usually no return path between transmitter and

receiver, the transmitter plays out the material without receiving

feedback from the receivers;

there is no capability to control data flow or re-transmitlost or corrupt data,

critical studio operations such as playout, outputmonitoring, video editing, etc., require streams withextremely low error rates,

less-critical operations such as video browsing can usestreams which require lower bandwidth and exhibithigher error rates,

42

The Stream Transfers of Data


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the mean reception frame-rate is dictated by the sendingframe-rate;

the transmission frame-rate is not necessarilyequal to the materials original presentationframe-rate, thus allowing faster or slower thanreal-time streaming between suitably configured

devices, and transfer from a transmitter to one or more receivers.

The received quality of a streamed TV signal is directlyrelated to the Quality of Service (QoS) of the data link. Fornetwork performance, QoS characteristics are measuredin terms such as:

bandwidth,

bit error rate,

jitter and delay (latency), and

access set-up time.

In streaming there is usually no return path to request aretransmission, so the receiver must make the best ofreceived data. There is no guaranteed quality; instead justthe so-called best effort. There are obvious similaritiesbetween data streaming and the transfer (pushing) ofdigital video via SDI or analog PAL/NTSC via analog links.

43

C H A P T E R 1 3

VideoConnection

A stream-receiver may join or leave atransmitted stream at any time without losing

information. Due to the missing return path to thetransmitter there is no capability for the re-transmission oflost or corrupt data. The received quality is directly related tothe Quality (of Service) of the data link. A Stream Transfer of

data is comparable to the transfer of digital video via SDIor analog PAL/NTSC over analog links. It therefore

fits the TV signal model very well.

S UMMAR Y


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A File is a collection of data or information that has aname, which is called the filename. All informationstored in a computer must be in a file. There are manydifferent types of files often defined for a specificapplication (computer program).

In the context of TV broadcasting, file transfer of

television program material involves each of the followingcharacteristics: there is a return path between the transmitter and the

receiver,

a file is both fixed and limited in length,

the moving or copying of a file, with the dominantrequirement that what is delivered at the destinationis an exact bit-for-bit replica of the original;

guaranteed delivery quality is achieved by means of theretransmission of corrupted or lost data packets,

in contrast to a stream transfer, the receivers may notjoin or leave the file transfer at any time. If the start orthe end of a file is not part of the received data, thewhole file will be lost.

the transmission rate may not have a fixed value and thetransmission may even be discontinuous;

although the transfer may often be required to takeplace at high speed, there will be no demand that itshould take place at a steady rate, or be otherwisesynchronized to any external event or process.

44

The File Transfers of Data


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An example is the transfer of a data file between diskservers. The conversion from stream to file and vice

versa is quite often automatically done in the background.When a certain scene or video clip is to be moved froma DVCPRO VTR to a server, the operator defines the inand out points through the time-code information

related to the first and last frames of the selected scene.After the operator or the control systems have started theVTR, a video and audio stream leaves the VTR via theSDTI output. At the in-point time, the server starts torecord the clip onto its hard disk(s). At this moment theserver assigns a filename to the clip and the disk-internal File Allocation Table (FAT) notes the point on thedisk where the data with this filename starts and wherethe clip ends. Within the hard disk, the FAT links theassigned filename to physical locations (addresses) on the

disk. It is now possible to move this video clip via filetransfer as defined above between disks or servers. Itis also possible to stream transfer the payload of this fileto a monitoring device or back to another VTR via an SDTIor SDI server output. At this moment the file is strippedof its filename and transferred as a stream to the otherdevices according to the rules defined in chapter 13.

Due to the fact that the transmission rate for the transfer of

a file may not have a fixed value and that transmission mayeven be discontinuous, file transfer doesnt suit the TVsignal model well. Although file transfer offers some

45

C H A P T E R 1 4

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advantages the easy use of standard IT-links for example we should not expect it to become a general replacementfor stream transfers in broadcast facilities. We shouldconsider file transfer more as a replacement for the manualtransport of videotapes, because you cant view orprocess the content during these two methods of transport.Both can be done in the background, by moving contentfrom one location to another.

46

There are five major differencesbetween a stream and a file transfer.

A file transfer requires a return path between

transmitter and receiver; a stream transfer does not. A file transfer does not require a specified connection

quality (QoS); the stream transfer does.

A file transfer guarantees that the content quality sent is thecontent quality received; a stream transfer only does its best.

A file transfer does not guarantee real-time transfer thatdepends on the selected QoS.

A stream-receiver can join or leave a transmitted stream atany time without losing information, the file-receivercannot.

File transfers will continue to be used inaddition to stream transfers but will notbecome a general replacement for

streaming.

S UMMAR Y


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Fiber Channel is a network that has been accepted as thehigh-performance computer peripheral interconnect andis very well suited for use in broadcast studioapplications. For these applications, Fiber Channel is

used by videodisk recorder vendors and for sharedstorage attachments. Commonly-available Fiber Channellinks support payload rates of about 100 Mb/s. Aspecial Fiber Channel Audio / Video (FC-AV) standard hasrecently been approved. Fiber Channel connections canbe based on a variety of transmission protocols includingSCSI, TCP/IP and ATM.

Despite the name, Fiber Channel can run over both cop-per and fiber media. The main tradeoffs are that

although longer distances can be achieved with fiber, itis more expensive. Speeds of up to 100 Mb/s can run onboth copper and fiber; higher rates require fiber media.

Fiber Channel defines three topologies, namely Point-to-Point, Fabric and Arbitrated Loop.

A Point-to-Point topology as shown in Figure 29A is the simplest of the three. It consists of only twoFiber Channel devices connected directly to each other.The transmit fiber of one device connects to the

receive fiber of the other device, and vice versa. Thereis no sharing of media, which allows the devices toenjoy the total bandwidth of the connection.

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C H A P T E R 1 5

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Fiber Channel


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The Fabric topology as shown in Figure 29B is anetwork topology based on cross-point switches toconnect up to 224 devices. The benefit of this topologyis that many devices can communicate at the same time;the media is not shared.

The Arbitrated Loop topology as shown in Figure

29C has become the most dominant, but it is also themost complex. Its a cost-effective way of connectingup to 127 ports in a single network without the needof a cross-point switch.

48

A

BSwitch

C

Fig. 29:Fiber ChannelPoint-to-Pointtopology (A)

Fiber ChannelFabric topology (B)

Fiber ChannelArbitrated Looptopology (C)


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The Fiber Channel data structure consists of Frames,Sequences and AV Containers:

Fiber Channel defines a variable length Frameconsisting of a label and a packet of up to 2,112bytes of data. That Frame is just a different name forour well-known packet and forms the basic unit ofcommunication between two devices. It is similar to thestructure of an Ethernet frame shown in Figure 10 of

chapter 4. A Fiber Channel Sequence is a series of one or more

related frames transmitted unidirectionally from onedevice to another. For each frame transmitted in aSequence, the sequence count information in the labelis increased by one. This provides a means for therecipient to arrange the frames in the order in whichthey were transmitted and to verify that all expectedframes have been received.

49

C H A P T E R 1 5

VideoConnection

Fiber ChannelNetwork

DVCPROServer

AddFiber ChannelNetwork Card

AddFiber ChannelNetwork Card

DVCPRONon-LinearEditing Systems

DVCPRO

Fig. 30:DVCPROinteroperabilitymaintains DVCPROquality via a FiberChannel network


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A single AV Container maps exactly into a single FiberChannel Sequence. The forthcoming Fiber ChannelAudio-Video (FC-AV) standard defines the mapping ofvarious digital video formats to Fiber Channel. Themapping is based on an AV container system. EachContainer is intended to hold the information of one TVframe. Data transported in a container is segregated intoObjects as shown in Figure 31B. An Object is acollection of data treated as a discrete entity. Objecttypes are for example video, audio or ancillary data.

50

EAV

SAV

SDTI Stream

HeaderData

SpaceSpaceType

DIF-Data

DIF-Data

Type

DIF-Data

DIF-Data

Type

DIF-Data

DIF-Data

Type

DIF-Data

DIF-Data

SDTI-Type

SignalType

DIF-ID

DIF-Data

DIF-ID

DIF-Data CRC

E

D

CDSPacket

CCDSPacket

CDSPacket

CDSPacket

CDSPacket

Payload

PacketLength

TimeStampDescriptor

Header

Header Object 0 Object 1 Object 2

SDTIinformation not used DVCPRO

Object 3

not used

Object n

not used

B

FC-AV Container 1 FC-AV Container 2 A

Informationtaken from theSDTI Header

Fig. 31:The Fiber ChannelAV-Container withDVCPRO content


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One of the possible Object types is a Compressed AVStream delivered via SDTI from a DVCPRO VTR. Theformat of a Compressed AV Stream is based on a FC-AVsub-container format shown in Figure 31C. The sub-container is composed of Stream Header and CompressedData Stream (CDS) packets. Figures 31C to 31E showhow the content for the CDS packet is taken from theSDTI stream for DVCPRO compression. Information forObject 0 (SDTI information) is taken over from the SDTIHeader of the SDTI stream, as explained in chapter 7.

In the 525/60 system one compressed AV Stream Object,which equals the information of one video frame, iscomposed of 750 CDS packets for 25 Mb/s DVCPROcompression. This number of CDS packets equals thenumber of SDTI data blocks over the period of an SDI

video frame.

51

C H A P T E R 1 5

VideoConnection

The high performance of a Fiber Channel networkmakes it ideally suited for connecting video servers and for

shared storage attachments. A special Fiber Channel Audio /Video (FC-AV) standard has recently been approved. TheArbitrated Loop structure has become the most

dominant Fiber Channel topology.

S UMMAR Y


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ATM, the Asynchronous Transfer Mode, which is anetwork technology based on asynchronous timedivision multiplexing, uses a small packet of a fixedsize. The small, constant size allows ATM equipment totransmit video, audio, and computer data over the samenetwork. The connection established by ATM is usually

unidirectional. Current ATM implementations supportdata transfer rates of from 25 to 622 Mb/s.

The most important and distinctive part of the ATMsystem is the packet. Since the packet has a specificlength, a new name has been given to it: a cell. Thereason for the new name was to avoid confusion. But for

you, the reader, it is more important to understand thata cell is just another packet. The ATM cell is 53 bytes,5 of which are for the header information and 48 for thedata payload. The actual cell payload in an ATM cell doesnot contain any error detection or correction. Each cellcontains a destination address and can be multiplexedasynchronously over a link.

ATM uses a star topology. All devices are connected to oneATM switch.

This switch directs incoming cells to the right output.ATM creates a fixed channel, or route, between two pointswhenever data transfer begins. When purchasing ATMservice, you can generally choose between four differenttypes of service:

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The ATM Wide Area Network


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Constant Bit Rate (CBR) specifies a fixed bit rate so thatdata are sent in a steady stream. This is analogous toa leased line.

Variable Bit Rate (VBR) provides a specified through-put capacity but data are not sent evenly. This is apopular choice for voice and video-conferencing data.

Unspecified Bit Rate (UBR) does not guarantee anythroughput levels.

Available Bit Rate (ABR) provides a guaranteedminimum capacity but allows data to surge at highercapacities when the network is free.

Synchronization between transmitting and receivingdevices is achieved through the transport of timingreferences within the stream. In order to stream contentbetween TV studios over a wide area, ATM is usedaccording to the so-called AAL 1 (ATM ApplicationLayer 1) specifications. Its Quality of Service providesConstant Bit Rate (CBR) and mechanisms for timingrecovery. Both of these are required for the synchronoustransmission of a TV signal via an asynchronous line. The

AAL 1 specification includes a Forward Error Correction(FEC) and byte interleaving mechanism that is capable ofrecovering up to four lost cells in a group of 128. This FEC

significantly improves the quality of the received stream.A number of suppliers offer ATM network access deviceswith SDTI interfaces.

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C H A P T E R 1 6

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All varieties of DVCPRO compression formats, covering bothSDTV and HDTV, can now be efficiently transported overATM. To make this possible, Panasonic developed amapping format from DV based programming materialto ATM.

This mapping format called ATM wrapper allows

faster than real-time or multi-program video streaming. Thesimultaneous transfer of four individual DVCPROprograms, the four times faster than real-time transfer ofa single 25 Mb/s program, and the real-time transfer ofDVCPRO HD can all be performed over an ATM link at155.52 Mb/s.

The layered structure of a DVCPRO network system isshown in Figure 32. The upper application layer isformed by DVCPRO. The middle layer is the adaptationlayer, which places the compressed AV stream into theFC-AV container as explained in chapter 15. The newWrapper Layer provides a generic mechanism for allkinds of video, audio, data and metadata and is thereforecalled the Common Layer.

54

Fig.32:Layer structure of aDVCPRO Network

DV-basedSDTI stream

Application Layer DVCPRO

Compressed AV stream(FC-AV container)

SDTI container

SDI transport Fibre Channel

ATM wrapper

AAL1

ATM

Streaming formatand/or

File transferformat

Other transportscheme (ex. 1394)

Adaptation Layers

Wrapper Layer

Transport Layer

Physical Layer

(chapter 1)

(chapter 7)

(chapter 11)

(chapter 14)


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Since the above-mentioned AAL1 process is carried outasynchronously, it is necessary to make video framesynchronization at this upper Common Layer.

This is done by defining a SYNC Stream Block (SSB),which is transmitted in one video frame period. Figure 33shows that the SSB consists of the SSB Header and one (or

more) FC-AV containers (explained in chapter 15). Morethan one container is used for faster than real-timetransmission or multiprogram transmission.

55

C H A P T E R 1 6

VideoConnection

Object 0SDTI

information

Object 2

DVCPRO

SSB HeaderFC-AV container 0

Header

FC-AV container1 to n

not used for DVCPRO 25

Fig. 33:Sync Stream Block(SSB) as ATMwrapper for theFC-AV container

The SSB Header contains such information as

SMPTE Universal Label,

length information,

number of containers,

number of programs, and

information related to the content of the container such as:

program number, and

container size.


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Due to the use of a generic ATM wrapper, which is based

on the FC-AV container model, TV signals of differentcompression formats can be transported via an ATM widearea network. Figure 34 shows an application example.

56

Relay station

Affiliatestation

ATMwide areanetwork

ATM unit

Productionstudio

ATMunit

Programcontent

transfer

Contribution

Fig. 34:Live streaming andcontent transfer overan ATM wide-areanetwork


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C H A P T E R 1 6

VideoConnection

ATMunit

Net-station

Home, office

Distribution

News, sport, event

HD camera

Bus for live relay

Relay point

ATM unit

Panasonic developed a mapping format fromDV based programming material to ATM. This mapping

format called ATM wrapper allows faster than real-timeor multi-program video streaming. A number of suppliers offerATM network access devices with SDTI interfaces.

All varieties of DVCPRO compression formats, coveringSDTV and HDTV, can now be transported efficientlyover ATM in accordance with its AAL 1

specification.

S UMMAR Y


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The IEEE 1394 bus was designed to support a variety ofdigital audio/video applications. Some of the applicationsare tailored to the consumer or industrial market. Theversion used in these environments relates to a specificcable and connector type, and is limited to cablelengths of about 4.5 m / 14' 9". Some companies have

announced cables that work of up to 100 m / 109 yd.The physical topology of IEEE 1394 is a tree ordaisy-chain network with up to 63 devices. Each device,or node, connected to the 1394 serial bus, supportsautomatic configuration. Each time a 1394 device isadded to or removed from the serial bus, the 1394 busreconfigures itself. This allows for hot plugging ofdevices and means that 1394 devices can communicate

with each other without needing a host system or busmanager. The physical connections between nodes aremade with a single cable that carries power and balanceddata in each direction. The 1394 serial bus provides fordiffering requirements by supporting data rates of 100, 200and 400 megabits per second. In the near future, the 1394serial bus will support data rates of 800, 1600 and 3200megabits per second.

Unlike most other protocols, IEEE 1394 provides thecapability for isochronous as well as asynchronoustransmission. Isochronous means a form of data trans-mission that guarantees a certain minimum data rate, as

58

IEEE 1394 More than just a Network for the Consumer Market


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required for time-dependent data such as video or audio.Isochronous can be contrasted with asynchronous, whichrefers to processes in which data streams can be broken byrandom intervals, and synchronous processes, in whichdata streams can be delivered only at specific intervals.Isochronous service is not as rigid as synchronousservice, but not as lenient as asynchronous service.

To transmit data, a 1394 device first requests control of thephysical layer. With asynchronous transport, theaddresses of both sender and receiver are transmitted,followed by the actual packet data. Once the receiveraccepts the packet, a packet acknowledgment is returnedto the original sender.

With isochronous transport, the sender requests an

isochronous channel with a specific bandwidth.Isochronous channel IDs are transmitted, followed by thepacket data. The receiver monitors the incoming dataschannel ID and accepts only data with the specified ID.

The bus sends a start indicator in the form of a timing gap.This is followed by the time slots for isochronouschannels, as shown in Figure 35. Whatever time remainsmay be used for any pending asynchronous trans-mission. Since the slots for each of the isochronouschannels have been established, the bus can guaranteetheir bandwidth and thus their successful delivery.

59

C H A P T E R 1 7

VideoConnection

Start indicator

Time slot forisochronous channel 1

Time slot forisochronous channel 2

Time slot forasynchronous packets

Packet frame = 125 microseconds

Time

Fig. 35:Isochronouschannels within anIEEE 1394 PacketFrame of 125microseconds


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The IEEE 1394 specification defines a basic mechanism forreal-time data transport, but does not establish theprotocols needed for specific application requirementssuch as transporting DVCPRO, DV or MPEG streams. Thisinformation is provided by the IEC-61883 protocol. Theprotocol covers three areas:

1. the Common Isochronous Packet (CIP) format,2. Connection Management Procedures for makingisochronous connections between devices, and

3. a framework for sending commands and controlsfrom one device to another.

A Common Isochronous Packet (CIP), as shown inFigure 36, is used to transport AV data. Common refersto the fact that this CIP is used for all kinds of AV data

(DV, DVCPRO, MPEG). In the following section, wewill refer to the DVCPRO implementation. A DIF block as explained in chapter 10 is the basic unit for alltransmissions over IEEE 1394. Each IEEE 1394 isochro-nous stream packet is composed of six DIF blocks, as-sembled without regard to DIF sequence boundaries.

60


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The IEEE 1394 Header contains such information asdata length, time-code and channel number. Isochronouspackets are not sent to a specific address but areidentified by a channel number.

The first two quadlets (32 bytes each) of the isochronouspayload constitute the CIP Header. The key bits are:

information regarding the source ID, indicatingwhere the data came from,

description of the data block size this is the onlyinformation which the receiving side needs to know inorder to reconstruct the original source packet,

compression format, and

raster format information.

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C H A P T E R 1 7

VideoConnection

IEEE 1394 Header (32 bytes)

Header CRC (32 bytes)

CIP HEADER(64 bytes)

Data = DIF blocks120 quadlets = 480 bytes

Header CRC (32 bytes)

Fig. 36:CommonIsochronous Packet(CIP) for transportover IEEE 1394


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Although the IEEE 1394 interface is primarily designed forconsumer devices including mini-DV camcorders and VTRs,Panasonic supports 1394 through its DVCPRO professionalvideo format. This allows desktop non-linear editingsystems to accept DVCPRO formatted video in thecompressed domain and edit the contents. The 1394interface was originally developed by Apple Computer andnamed FireWire. i-Link and other brand names are alsoused, but these names are basically interchangeable asIEEE 1394 for consumer use. However, the DVCPROimplementation of 1394, referred to as the DVCPROTerminal, differs in three important ways from otherimplementations:

the DVCPRO data stream uses locked audio whereasconsumer video data may use unlocked audio as well,

the part of the CIP Header which identifies the DV datais different for the DVCPRO data stream, and

the DVCPRO and DV data stream for 60Hz field ratefollows the 4:1:1 sampling structure. 50Hz field rateDVCPRO uses 4:1:1, wheras consumer DV uses 4:2:0.

62

IEEE 1394 devices allow for hot plugging andcan communicate with each other without needing a

bus manager. IEEE 1394 provides the capability forisochronous transmission, guaranteeing a reserved

bandwidth for the data transport. Panasonic supports 1394through its DVCPRO professional video format. This allows

desktop non-linear editing systems to accept DVCPROformatted video in the compressed domain and edit

the contents.

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Chapter 13 & 14 dealt with the differences betweenfile- and stream-transfers. To use the benefits of a filetransfer the guaranteed delivery of all bits and bytes it is mandatory to standardize one File Exchange Formator to at least document a limited number. A FileExchange Format can be moved between devices from

different vendors over different types of transport. It ismore complex than a file format that is created within acomputer to store parts of an incoming video stream onits own attached storage devices.

One can say that the file stays on top of a softwarepyramid, as shown in Figure 37.

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C H A P T E R 1 8

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The Universal File Exchange Format

TypeofCPU(HW)

operatingsystem(SW)

fileformat(SW)

executableprogramm(SW)

Fig. 37:The software

pyramid


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Innovation cycles are becoming shorter and shorter. Thisaffects hardware (CPUs), operating systems, applicationprograms and, of course, file formats. If you have ever triedto read a document-file you wrote 10 years ago with thelatest version of your word processing program, youll

know why. The latest software simply tells you: I cant openthis file! This is not acceptable in broadcast applications forfiles containing program content.

The foundation of the software pyramid is determined bythe CPU type used. If you change the CPU type you haveto change the Operating System as well. The executableprogram the .exe files sit on top of the operatingsystem. They form the applications and define their ownapplication dependent file formats. That means that youcant usually replace one of the building blocks below thefile format without affecting the file format itself(Figure 38).

64

TypeofCPU(HW)

Operatingsystem(SW)

Fileformat(SW

) Executableprogram(SW)

Executableprogram(SW)

Fig. 38:Removal of a lowerlayer may affect the

file format


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On the other hand, computer-based technology hasalready proven its usefulness in many applications withinthe professional broadcasting environment. Prominentexamples can be found worldwide in the area of server-systems for production, post-production, playout andarchiving.

The common denominator in all these applications is thetransport of program data and storage on non-linearmedia on the basis of proprietary file formats. TheEuropean Broadcasting Union has already expressed astrong requirement to share files between systems fromdifferent manufacturers, both within the studio andbetween different broadcast facilities.

The expected operational and economic benefits of

adopting exchange in file-form can briefly besummarized as follows:

File exchange avoids the possibility of introducing anypicture quality degradation during the data transportdue to the Guaranteed Delivery of all bits and bytes(see chapter 14),

Metadata, audio, video and data can be transferred inone common wrapper,

Systems can be built using general computer

equipment, an economic benefit to overall systemcosts etc., and

The transmission rate may not have a fixed value andthe transmission may even be discontinuous;

this enables economic file transport in the backgroundthrough the use of unoccupied bandwidth in availablenetworks. There is no demand for it to take place at asteady rate, or be otherwise synchronized to anyexternal event or process.

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Any File Exchange Format should be well defined and inthe public domain. Panasonic fully supports this view.

Work is going on in various trade and standardsorganizations to fulfill these requirements.

The general structure of any AV-file, as shown in Figure39, consists of:

a preamble:

label,

table of file content, and

general metadata to describe the information located in

the body,

Organizations like EBU are particularly concerned aboutprogram exchange between their members. In the past thistook place via an exchange of recorded videotapes. Thatis why recording standards were so important. In future,the exchange of programs may take place via file transferdepending on the cost of wide area network services.

EBU experts have requested that a future common fileformat should not be related to any specific hardware(CPU) or operating system. It should not be payloadspecific and support the mapping of all majorcompression schemes into the file body.

66

Preamble Body Post-amble

Label Allocationtable

Generalmetadata

Content = essence + metadata

DVCPRO, MPEG, metadataEOF

Fig. 39:General structure ofan AV-file


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the file body itself, into which payload data such asuncompressed or compressed video, audio, data andadditional metadata is mapped, and

a post-amble with an end of file (EOF) marker.

Although file transfer offers some advantages, we should

not expect it to replace stream transfer. A receiver may joinor leave a stream at any time, which allows the receiverto select only a part of the content delivered via thestream. The file structure shown in Figure 39 does notpermit the so-called partial file access. If required, the fileheader information has to be repeated within the streamin adequate intervals to permit receivers to synchronizeitself onto transfers already in progress. This makes thefile structure much more complex.

The above-explained basic structure is not ideal forarchiving programs on tape either. To search for acertain program, it is necessary to recover the metadatafirst. Therefore, it is preferable to store the metadata ona different, separate storage medium, which providesmuch shorter access times than tape. The metadataprovides a link to the content on tape and vice versa.

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Work is going on to define a File Exchange Formatthat is independent of any specific hardware or vendor.

We may not see a universal File Exchange Format that coversall applications. Different applications naturally have different

requirements. Though file transfer offers some advantages,we should not expect it to replace stream transfer.

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The use of modern IT infrastructures increases the

efficiency of broadcast facilities. A prerequisite for this was

the transformation of the digital TV signal of the Serial

Digital Interface (SDI) into a truly data signal. The

Serial Digital Transport Interface (SDTI) laid the

foundation for that transformation. Now networking

technologies can be applied which allow sharing and

transport of content between individual devices andusers. Due to the fact that DVCPRO already records true

data packages, it is well prepared for this data world, as

shown in Figure 40. Table 1 summarizes the typical

properties of the Network-Interface Types and Network-

Containers discussed in this book.

68

Conclusion

Studio B

ATMunit

FiberChannel

ATMwide areanetwork

ATMunit

FiberChannel

SDTISDTI

IEEE1394IEEE1394

Microwave, satellite

Studio A

Inside facility

Short distance

Long distance

Fig. 40:DVCPRO loss-lessContribution Network


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VideoConnection

SDTI

Desktop

LAN

WAN

Streamtransfer

File transfer

Uni-directional

Bi-directional

Guaranteedbandwith

Quality ofService

Propertiesin main

application

Main

application

Studio-synchronous

Isochronous

Asynchronous

Can CarryDVCPRO

Ethernet FiberChannel ATMIEEE1394

Table 1:Network-InterfaceTypes and Network-Containers


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12) SMPTE 354M-2001 Television ATM Common Layer forTransport of Packetized Audio, Video and Data over

Asynchronous Transfer Mode (ATM) using ATM AdaptionLayer Type 1 (AAL 1).

13) Hans Hoffmann, Interfaces, Protocols and Inter-operability in TV Production & Archiving, 1st Management

Symposium Cologne, May 2000.14) EBU Technical Statement D89-2000: Quality andinteroperability in a 625/50 digital television productionenvironment using MPEG compression.

15) Steve Steinke, ATM Basics, LAN Magazine/NetworkMagazine, May 1995.

16) Charles L. Hedrick, Introduction to the InternetProtocols, Rutgers University 1987.(http://oac3.hsc.uth.tmc.edu/staff/snewton/

tcp-tutorial/index.html)17) Gary Hoffman and Daniel Moore, IEEE 1394:

A Ubiquitous Bus, COMPCON 95.

18) University of New Hampshire InterOperabilityLaboratory, Fiber Channel Tutorial.(http://www.iol.unh.edu/training/fc/fc_tutorial.html)

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19) WPI Department of Electrical and ComputerEngineering: ATM Specifications(http://www.ece.wpi.edu/courses/ee535/hwk10cd95/

bkh/specs.html20) T11/Project 1305-D/1.4, Fiber Channel - Audio

Video (FC-AV), Working Draft, September 17, 2000.(ftp://ftp.t11.org/t11/pub/fc/av/00-252v3.pdf)


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AAL 1 53

AES 22

ANSI/SMPTE 259M 12

Asynchronous 52, 59

ATM 47

Compression 13

Container 26

Content package 39

CRC 16

D1 - VTR 9

Datagram 17

Destination address 16

DIF 31

DV 13

DVCPRO 13

End of Active Video (SAV) 19

Ethernet 15European Broadcasting Union (EBU) 27

FC-AV 47

File exchange 63

File transfer 29, 44

FTP 17

IEEE 1394 58

Isochronous 59

Length/Type 16

LAN 15

Layer 6

Mapping 33

MPEG-2 13

Network 15

Payload data 16

Physical layer 11

Protocol 15

Quality of Service (QoS) 43

SDTI 23

SDTI-CP 39

Serial Data Transport Interface 23

Serial Digital Signal (SDI) 10

Server 45

SMPTE 3

Society of Motion Picture

and Television Engineers 6

Source address 16

Start of Active Video (SAV) 19

Stream transfer 42Synchronous 59

WAN 29

Index


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Panasonic 2001

Matsushita Electric Industrial Co., Ltd.

Video Systems Division

Contacts:

USA

Panasonic Broadcast & Digital Systems Company

3330 Cahuenga Blvd W.

Los Angeles, CA 90068

phone +1-323-436-3500

email [email protected]

United KingdomPanasonic Broadcast Europe Ltd.

West Forest Gate, Wellington Road

Wokingham, Berkshire, RG40 2AQ

phone +44-118-902-9200


Germany

Panasonic Broadcast Europe GmbH

Hagenauer Str. 43

65203 Wiesbaden

phone +49-611-18160


Japan

Matsushita Electric Industrial Co., Ltd.

Video Systems Division

2-15 Matsuba-cho, Kadoma, Osaka, 571-8503 Japanphone +81-6-6905-4675



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Production:

AV MEDIA TECHNOLOGY - Consultants -

Ringstrasse 9

64342 Seeheim-Jungenheim

Germany

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