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Quantitative Comparison of H.264/AVC and VP8 Video Codecs for Video Conferencing

Quantitative Comparison of H.264/AVC and VP8 Video Codecs for Video Conferencing. Scott Kristjanson CMPT-820 Multimedia Systems Instructor: Dr. Mohamed Hefeeda Dec 2 nd 2010 . Presentation Overview. Project Overview Methods Results Conclusions Future Work References.

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Quantitative Comparison of H.264/AVC and VP8 Video Codecs for Video Conferencing

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  1. Quantitative Comparison of H.264/AVC and VP8 Video Codecs for Video Conferencing Scott Kristjanson CMPT-820 Multimedia Systems Instructor: Dr. Mohamed Hefeeda Dec 2nd 2010

  2. Presentation Overview • Project Overview • Methods • Results • Conclusions • Future Work • References

  3. Project Overview • Compare Video Codecs for use with Video Conferencing: • VP8 – by Google’s WebM project • H.264/AVC – used x256 Open Source Codec

  4. VP8 Overview • Video Codec owned by Google and made open Source • WebM Project: Matroska container with VP8 video and Vorbis audio • VP8 - Earlier versions VP7 (Skype), VP6 (Flash Video), VP3 (Theora) • Key Features: • Adaptive Loop Filtering – Identifies Fast/Slow/Static regions and adapts encoding to match for improved quality/performance • Golden Frames – for storing reference point to background layer. Can be used for reference without display them. • Faster encoding time by avoiding use of Arithemetic VLE (CABAC). • Dynamically scales resolution. No need to involve application, encoder decides. No I-frame required as a transition point. • Structure: • Frame same as H.264, Segment like a Slice • Partitions used to separate critical data from video data • I-Frame, P-Frames, Golden-Frames, no B-Frames due to Patents For more information, see Google’s “Intro to VP8” slides at: http://www.slideshare.net/DSPIP/google-vp8

  5. Methods • Quantitative Comparison: Invoke encoders/decoders with various presets: • Manually from DOS, then use YUV_Compare to compute Y-PSNR • ViCoS Codec Comparison utility from MSU – gives ranking only • Used sequences foreman and salesman to simulate video conference calls • Encode with bit rates 100, 800, 1500 kbps to produce bit rate curves Extract Quantitative Data • Y-PSNR – Signal to Noise Ratio for Luminosity • Y-SSIM – Structural Simularity Data for Luminosity • Encoding Time • Frame Rate • Bit Rate • Qualitative Comparison • View original YUV file and encoded/decoded files using YUVviewer • Test VP8 in Video Conferencing System to verify Quantitative Data

  6. Reference Video Sequences • Salesman • Ideal choice for simulating video conference • Not used since not available in CIF format • Tried to convert from .avi to CIF format but ran out of time • Foreman • Good choice, but with some background movement • Used in detailed quantitative analysis • Used with Vicos for codec over-all evaluation • Mobile • Slow motion with detailed cartoon-like background • Used with Vicos for codec over-all evaluation • Stefan • Lots of motion and lots of background detail • Used with Vicos for codec over-all evaluation

  7. DOS Command Line Testing • x264 encode/decode: • vp8 encode/decode: Visually compare original video to encoded video with YUV_Viewer

  8. PSNR Computing Y-PSNR with AviSynth • AVS script to read and compare two YUV files: • Encoded/Decoded YUV video from DOS command line testing • Original YUV video • yuv_compare_foreman.avs • foreman_yuv_compare.log loadplugin("C:\megui\tools\avisynth_plugin\rawsource.dll") decodedClip = RawSource("C:\foreman_352x288_decoded_vp8.yuv",352, 288, "I420") originalClip = RawSource("C:\foreman_352x288.yuv", 352, 288, "I420") Compare(decodedClip, originalClip, "YUV", "foreman_yuv_compare.log") Mean Max Max Absolute Mean Pos. Neg. Frame Dev. Dev. Dev. Dev. PSNR (dB) ----------------------------------------------------- 0 0.7591 +0.0252 5 -3 47.6277 1 0.7566 -0.0050 5 -4 47.6655 … … … … … … 299 0.8597 +0.0070 4 -4 46.8949 Total frames processed: 300 Minimum Average Maximum Mean Absolute Deviation: 0.6941 1.2438 3.7930 Mean Deviation: -0.2703 -0.0194 +0.0527 PSNR: 33.2940 44.9776 48.2338 Overall PSNR: 41.3285

  9. MSU’s Video Codecs Scoring System (ViCoS) • Allows custom Codecs to be bound in and tested • bind in encoders and decoders (x264 and vp8) • define encoding and decoding parameters and presets to be tested • encodes/decodes test sequences automatically and computes distortion • generates relative ranking and relative scores for PSNR and SSIM only • Versions: • Demo version used – provides ranking scores only • Professional version – creates PNSR/SSIM charts automatically

  10. Video Quality – Peak Signal to Noise Ratio (Y-PSNR) • Bit-Rate/Quality Trade-Off: • 100kbps – Poor Quality • 800kbps – Acceptible to good • 1500kbps – Very Good to Excellent PSNR Ranges: 38+ Excellent 36-37 Very good 34-35 Good 26-33 Poor 25 or less Garbage

  11. Video Quality – Structural Simularity (SSIM) • SSIM score under 0.95 is quite noticible: • 100kbps – Poor Quality for all codecs (especially x264 Fast Zero-Latency & Ultrafast) • 800kbps – most codecs Acceptible to good (except VP8 RT CBR and x264 Ultrafast) • 1500kbps – all Very Good (except x264 Ultrafast)

  12. Encoder Frame Rates • x264 Encoder significantly faster than VP8 for similar Quality

  13. Codec Preset Good Codec Presets for Video Conferencing • Need min of 15 fps for Video Conferencing, prefer 30 fps • Want decent quality – Y-PSNR of 34 or better • Low Latency: under 150ms required • 4 Presets met these requirements:

  14. Conclusion • VP8 and x264 provide similar video quality • For higher bit rates, x264 PSNR better by 2% • For lower rates, VP8 wins by almost 10% • x264 provides better performance in some cases • x264 is between 36% and up to 2x faster than VP8 • A big improvement! VP8 used to be 5-20 times slower!

  15. References: • [1] Image Quality Assessment: From Error Visibility to Structural Similarity • Zhou Wang, Alan Conrad Bovik, Hamid, Rahim Sheikh, and Eero P. Simoncelli • IEEE Transactions on Image Processing, Vol 13, No. 4, April 2004 • http://ieeexplore.ieee.org.proxy.lib.sfu.ca/stamp/stamp.jsp?tp=&arnumber=1284395 • [2] 6th Annual MPEG-4 AVC H.264 video codecs comparison • D. Vatolin, D. Kulikov, and A. Parshin, April 2010 • http://compression.ru/video/codec_comparison/h264_2010/

  16. Backup Slides

  17. H.264/AVC Presets Used • Codecs tested with various presets and tunings • Looking for good balance of quality and speed for video conferencing • Each tested with 3 target Encoding bit rates: 100, 800, 1500 kbps • x264 Presets: • Placebo • 2-Pass Slower Encoding Speed, higher quality • Fast (tested with 2 tunings) • 2-Pass Faster Encoding Speed, good quality • 2-Pass tuned with zero latency specified • Default • 1-pass with default settings • Baseline • 1-pass fast encoding but poor quality at lower bit rates • Ultrafast • When speed is all that matters!

  18. VP8 Presets Used • Best • 2-Pass encoding • Maximimizes Quality but slower encode times • Good 2-Pass • 2-Pass encoding, less quality but faster encode times • measured with 1, 2, and 4 cpu cores specified • Good 1-Pass • 1-Pass encoding, less quality but faster encode times • Fast VBR • 1-Pass variable bit-rate fast encoding • RealTime CBR • Encoder Frame buffer size 6 • with and without deadline specified

  19. VP8 Support for MultiCore Processors

  20. Encoding Bit Rate vs Target Bit Rate • Both Codecs appear to over-run target slightly • VP8 tracks to target bit-rate slightly better

  21. Video Quality – Structural Simularity (SSIM) • SSIM score under 0.95 is quite noticible: • 100kbps – Poor Quality for all codecs (especially x264 Fast 0-Latency and Ultrafast) • 800kbps – most codecs Acceptible to good (except VP8 RT CBR and x264 Ultrafast) • 1500kbps – all Very Good

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