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Yossi Cohen

Video Transcoding & Transrating

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Overview

Full TranscodeOpen Loop transratersCoefficient Drop TransraterRe-quantization transrater

Closed loop transraterFPDT

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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

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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

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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

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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.

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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

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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

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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

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

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Quality / CPU comparisonLine – Quality, Bar – CPU Cycles

Full T

ranscode

Aided T

ranscoder

FP

DT Re-

Qua

ntization

transrater

Coefficien

t D

rop

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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

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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

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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

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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