Video Tanscoding and Transrating methods review and comparison

1. Video
Transcoding
& Transrating
Yossi Cohen
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2. Overview
 Full Transcode
 Open Loop transraters
Coefficient Drop Transrater
Re-quantization transrater
 Closed loop transrater
FPDT
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3. Full Transcoder
 Full transcoding does full encoding and
decoding of the video. Features include:
Easy Implementation
Usually used for
 format conversion such as MPEG2 Video->H264
 Video Resize and frame rate reduction
Highest CPU requirements
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4. Aided Transcoder
 Full decoding of the video
 Encoding Video while re-using the decoded video
information including:
Qp selection
Motion vectors
Block size (8x8, 4x8 etc.) selection
MV, Qp
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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
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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.
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7. Coefficient Drop Transrater
 Performs only Entropy Decoding/Encoding
 Drops some of the coefficients according to
psycho-visual models.
 Features
 Fastest transrater
 Poorest video quality per bitrate
 Introduce drift
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8. Re-Quanitzation transrater
 Performs Entropy decoding and dequantization followed by quantization with
an Higher Qp (lowers quality & BR)
 Features
 Fast Transrater
 Poor video quality per bitrate
 Introduce drift
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9. Closed loop transrater (FPDT)
 Performs Entropy decoding and dequantization 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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10. Closed Loop Transrater - Features
 Faster then Transcoders
 No drift
 Quality is transcoder grade per same bitrate
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11. Quality / CPU comparison
 Line – Quality, Bar – CPU Cycles
Coefficient
Drop
Re-Quantization
transrater
FPDT
Aided Transcoder
Full Transcode
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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
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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
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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
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15. Thank you!
More About me:
 Video Expert
 Lectures on Video / Android / VoIP
 Android Native Developer
Yossi Cohen
yossicohen19@gmail.com
http://www.mobilevideotech.com
+972-545-313092
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