Keeping Video Quality Pristine throughout the Production Process: - - PowerPoint PPT Presentation

Keeping Video Quality Pristine throughout the Production Process: 4:2:2 10-bit AVC/H.264 encoding

Pierre Larbier ATEME (Burbank, USA & Bievres, France)

Agenda

• Current States
• Talk about the AVC/H.264 4:2:2 10-bit profile
• Empirical comparisons against 4:2:0 8-bit &

4:2:2 8-bit

• Multi-Generation Encoding
• Production Cases

2

Production & Transmission Processes

• Production uses 4:2:2 10-bit over SDI

– Used in video editing, tape decks, file storage, etc – Video needs to be transmitted by internal system or across networks

• Today’s transmission mostly uses

– 4:2:0 8-bit (MPEG-2 or AVC/H.264) for consumer applications – 4:2:2 8-bit(MPEG-2) for contribution applications

• 20-60 Mbps with latency from 1 sec-250ms

3

AVC/H.264 Studio Profile VS. Current Implementations

• Most AVC/H.264 products are currently geared

towards consumer video market

– 4:2:0 8-bit and <30Mbps encode rates @ High Profile – Using this equipment will necessitate resampling & incur mismatching if used for production transmission applications

• High 4:2:2 Profile

– Can handle 4:2:2 processing @ 10-bit and is ideal for production transmission applications – Can handle upto 200 Mbps(HD) and 40 Mbps (SD)

4

About 4:2:0 Compression

• Professional video sources are 4:2:2
• 4:2:0 compression requires resampling filters

5

• Progressive and Interlace chroma location schemes are different
• Challenges for existing chroma resampling architecture:
• Possible mismatch between the 2 resampling filters
• Resampling filters quality not guaranteed
• Choosing between Progressive and Interlace filters is not obvious

4:2:2 4:2:2 → 4:2:0 Downscaling 4:2:0 Encoding 4:2:2 4:2:0 → 4:2:2 Upscaling 4:2:0 Decoding SDI SDI Encoder Decoder

4:2:0 Chroma Artifacts

• Mainly caused by a mismatch between downscale/upscale filters
• Color bleeding
• Chroma detail loss
• Interlace/Progressive artifacts
• Worsen with each generation
• Difficult to control in a Production chain

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After 5 4:2:2 ↔ 4:2:0 conversions Source picture

Detail Loss Color Smearing Interlace artifacts

About 4:2:2 Compression

• At the 1st generation, with perfect resampling filters, 4:2:2 and 4:2:0
• verall quality is roughly the same:

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• But in multi-generation and/or with mismatched sampling filters,

4:2:2 quality is much better than 4:2:0

CrowdRun, 1080i25 33 35 37 39 41 43 45 47 49 20 40 60 80 100 120 140 160 180 200 220 Bitrate (Mbps) Combined PSNR (dB) 4:2:0 4:2:2

4:2:2 vs 4:2:0 with perfect resampling filters

Current 8-bit Compression

• Professional video sources are 10-bit
• 8-bit compression requires rounding before compression

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• Motion compensation and loop-filtering performed using 8-bit samples
• Challenges for 8-bit architecture:
• Scalers match and quality not guaranteed
• Reduced accuracy in the encoding process reduces coding efficiency
• Luma shift caused by lack of rounding control

10-bit 10-bit → 8-bit Downscaling 8-bit Encoding 10-bit 8-bit → 10-bit Upscaling 8-bit Decoding SDI SDI Encoder Decoder

10-bit compression: banding removal

• Processing video with 8-bit sample depth may create banding artifacts in

shallow changing light scenes:

• Blue skies
• Underwater scenes
• Sunsets
• These defects are not visible at 10-bit or more

9

10-bit compression 8-bit compression

Banding artifacts

10-bit compression: increased coding efficiency

• Coding efficiency is increased: less bit-rate for the same quality
• Rate saving between 5% and 20% on most sources
• Most of the gain is provided with 10-bit coding. With 12-bit and 14-bit,

coding efficiency gain is there but much smaller

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Woman with a Bird Cage, 1080i30 28 30 32 34 36 38 40 42 44 46 48 50 15 30 45 60 75 90 105 120 135 150 Bitrate (Mbps) PSNR Y (dB) 8 bit 10 bit 12 bit Woman with a Bird Cage, 1080i30 0.00 0.10 0.20 0.30 0.40 0.50 0.60 20 40 60 80 100 120 140 160 180 200 220 Bitrate (Mbps) PSNR Y gain relative to 8-bit (dB) 10 bit 12 bit

RD curve at 8,10 and 12-bit Distortion gain vs 8-bit compression

10-bit compression: artifacts reduction

• 10-bit compression reduces 3 kind of artifacts:
• Contouring
• Smearing
• Mosquito noise
• As a side-effect, 10-bit compression also reduces random distortion of

shallow textured objects (clouds for instance)

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Contouring Mosquito Noise

8-bit compression 10-bit compression

AVC H422P vs MPEG-2 422P

• H.264 H422P outperforms MPEG-2 422P in Contribution applications:
• 10-bit support
• More than 20Mbps saved at Contribution rates!

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CrowdRun, 1080i25 28 30 32 34 36 38 40 42 44 46 20 40 60 80 100 120 140 160 Bitrate (Mbps)

Combined PSNR (dB)

MPEG-2 AVC/H.264

Woman with a Bird Cage, 1080i30 38 39 40 41 42 43 44 45 46 47 48 49 50 51 20 40 60 80 100 120 140 160 Bitrate (Mbps)

Combined PSNR (dB)

MPEG-2 AVC/H.264

Example 2 Example 1

GOP Structure Types for Contribution

• GOP structure needs to be carefully considered
• Possible Contribution GOP Structures

– Intra-only, AVC-I, Short GOP, Adaptive Long GOP

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32 34 36 38 40 42 44 46 48 50 20 40 60 80 100 120 140 160 180 200 Average PSNR Y Bitrate (Mbps) Into Tree, 1080i25 AVC-I 100 Intra Only IbBbI Long GOP

Importance of GOP structure on coding efficiency

• Adaptive Long GOP and Short GOP give

better performance at same bit rate

• Guide: let encoder make picture type

decision wherever possible

Role of GOP in Multi-Generation Encoding

• 3-4 Re-encodes can happen in a production transmission workflow path
• Aligning Encodes at GOP Boundaries can retain quality

– PSNR Drop 3dB (Aligned) Vs 5dB (non-aligned) @ 7th GEN

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27 28 29 30 31 32 33 34 35 36 1 2 3 4 5 6 7 Average PSNR Y (dB) Generation ParkJoy 1080i25 @ 60Mbps - Aligned GOP I IbBbI Long GOP 27 28 29 30 31 32 33 34 35 36 1 2 3 4 5 6 7 Average PSNR Y (dB) Generation ParkJoy 1080i25 @ 60Mbps - Unaligned GOP I IbBbI Long GOP

Multiple generations with aligned GOPS Multiple generations without aligned GOPS

Production Uses

• Remote Truck Uplinks

– Transmit in AVC 422 10-bit and at lower bit rates than MPEG-2 422P

• Playout to Tape Infrastructures

– Easily integrate transmission back into an SDI infrastructure (international applications)

• Remote Collaboration

– Realtime 422 10-bit at lower bit rates

• Multiple Generations Re-encodes

– Typical Streams can re-encode 3-4 times before it gets to consumer, so transmission in 422 10-bit aligned GOP will preserve quality

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Advantages

• Significantly lower transmission costs
• Improve video quality on existing transmission links

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Summary

Using 4:2:2 10-bit allows:

• Process original source video in as close to an original form
• Enables most demanding application in terms of quality & rate
• Offers significant gain in quality and/or rate over existing solutions
• Reduces banding, smearing, and mosquito noise
• Retains quality in production processes
• Integrates into an SDI infrastructure at highest allowable quality

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Thank-You

p.larbier@ateme.com