video transcoding transrating

1

Yossi Cohen

Video Transcoding & Transrating

2

Overview

Full TranscodeOpen Loop transratersCoefficient Drop TransraterRe-quantization transrater

Closed loop transraterFPDT

3

Full TranscoderFull transcoding does full encoding and

decoding of the video. Features include:Easy ImplementationUsually used for

format conversion such as MPEG2 Video->H264Video Resize and frame rate reduction

Highest CPU requirements

4

Aided TranscoderFull decoding of the videoEncoding Video while re-using the decoded video

information including:Qp selectionMotion vectorsBlock size (8x8, 4x8 etc.) selection

MV, Qp

5

Aided Transcoder Features

High CPU requirements Like Full transcoder, enables:

Resizing Change of Frame type (P->I, I->P) for sync point changing Smooth frame rate conversion Accurate (no drift) transcoding

6

Open Loop Transcoders

Open loop transcoders are fast and simple transrater.

Open-loop – does not correct the drift error created by the transrating on next frames

Introduces drift error into the video – video quality seriously degrades as a function of the distance from last I frame.

7

Coefficient Drop Transrater

Performs only Entropy Decoding/EncodingDrops some of the coefficients according to

psycho-visual models.Features

Fastest transraterPoorest video quality per bitrate Introduce drift

8

Re-Quanitzation transraterPerforms Entropy decoding and de-

quantization followed by quantization with an Higher Qp (lowers quality & BR)

FeaturesFast TransraterPoor video quality per bitrate Introduce drift

9

Closed loop transrater (FPDT)Performs Entropy decoding and de-

quantization followed by quantization with an Higher Qp (lowers quality & BR)

Adds quantization error from previous frame to next frame to avoid drift

Error Store

10

Closed Loop Transrater - Features Faster then TranscodersNo driftQuality is transcoder grade per same bitrate

11

Quality / CPU comparisonLine – Quality, Bar – CPU Cycles

Full T

ranscode

Aided T

ranscoder

FP

DT Re-

Qua

ntization

transrater

Coefficien

t D

rop

12

Frame dropping overview

Frame dropping could improve KPI (5-10%) and reduce CPU load.

Smooth frame drop – convert to any fps, fixed deltaT between frames, frame interpolation. Very high CPU requirements

Regular frame drop – drop any frame introduce some jerkiness

Limited fps – cant drop any frame, introduce higher jerkiness

13

Frame Dropping -2

Transcoders support both Regular frame drop

Transraters only supports limited fps frame drop

FPDT transrater might support regular frame drop at additional development time

14

Frame Resize

Frame Resize could considerably lower bitrate.

CPU - Requires per pixel operations for resizing – higher CPU but lower encoded frame size which lowers CPU.

Transcoder could easily support resize – additional CPU requirements

FPDT could support resize but would cost considerable CPU and development time

15

Thank you!

Video Expert

Lectures on Video / Android / VoIP

Android Native Developer

More About me:

Yossi CohenYossi Cohenyossicohen19@gmail.comhttp://www.mobilevideotech.com

+972-545-313092+972-545-313092