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October 22, 2013

Next Generation Video Codecs: HEVC, VP9, Daala

Nowadays video services (digital television, Internet video etc.) are a common part of our live. According to Cisco [1] mobile video traffic was 51 percent of the entire global Internet traffic by the end of 2012 and it is expected to be 66 percent by 2017.
The demand on video and its quality is very high. Since the appearance of VoIP in 1984 video resolution has increased from QCIF (176×144 pixels) to Full HD (1920×1080). Now it is evolving to 4K (3840×2160) and 8K (7680×4320) UHD. But the higher the resolution and quality is, the higher bitrate it takes.
This paper contains a general review of new video compression standards HEVC, VP9 and Daala. Their compression efficiency is studied and compared to AVC.
The paper was reported at the XI International Theoretical and Practical Conference of Students and Young Scientists "Youth and Contemporary Information Technolodies". The report can be found here.

HEVC

High Efficiency Video Coding is an evolution of current industrial H.264/AVC standard [2]. AVC was adopted in 2003 and determined the development of HD television. HEVC was developed to increase AVC compression efficiency by two times and endorse the development of UHD systems. HEVC is expected to replace AVC in newly developed video systems.
H.265/HEVC [3] is still a block-based DFT codec with the same general design. One of the main improvements is the increase of maximal block (called Largest Coding Unit - LCU) size from 16×16 to 64×64 pixels. It aims to improve the efficiency of block partitioning on high resolution video sequences (bitrate savings are about 16% [4]). Larger blocks provoke the introduction of quad-tree partitioning with adaptive block sub-splitting and adaptive prediction units and transform units partitioning. Additional 25 intra prediction directions were added to improve intra-frame coding efficiency. Also there came more motion vector prediction candidates and several other modifications to improve inter-frame compression performance.

VP9

Superior video compression efficiency of HEVC is able to provide network usage savings, which should be of a great interest to Google YouTube video service. The development of free-to-use video compression standard with the efficiency comparable to proprietary HEVC could become financially successful. That came one of the reasons for Google to create VP9 [5] compression standard.
Google VP9 basically shares common features with AVC coding like VP8 did. The main evolutional change is also the increase of largest block (called 'super block') size up to 64×64 pixels and its adaptive sub-splitting. Motion vector prediction was improved, unlike intra prediction that still has only 10 modes.

Daala

Unlike HEVC and VP9, Daala [6] is being designed to step aside common video compression techniques. Among the key distinctive features there are lapped transforms instead of block-based DFT, lifting pre- and post-filtering instead of deblock filtering, frequency domain intra prediction, Time/Frequency Resolution Switching etc.
The development of Daala codec is still in progress. It is designed patent free and might potentially become the next generation video codec in 5-10 years if the novel techniques would prove to be successful.
Comparison results For comparison purposes open-source implementations of the reviewed codecs are used. HEVC compression efficiency is measured with HM Test Model. Verification of coding parameters is done with Elecard HEVC Analyzer [7]. For AVC estimation JM reference encoder and Elecard Stream Analyzer [7] are used. Both JM and HM utilize rate-distortion optimization (RDO) techniques to achieve quasi-optimal correlation between compression rate and quality. Both encoder implementations are evaluated in “constant quantizer” mode.
H.264/AVC is an industrial video compression standard at the moment. It was adopted in 2003 and determined the development of HD television. In April 2013 next generation video compression standard H.265/HEVC appeared. It was developed by JCT-VC to increase AVC compression efficiency by two times and endorse the development of UHD systems. As AVC the new standard is proprietary and thus its usage in not free That's one of the main reasons for development of Google VP9 compression standard. Being free from patent claims VP9 should achieve similar compression rates as HEVC.

Comparison results

For comparison purposes open-source implementations of the reviewed codecs are used. HEVC compression efficiency is measured with HM Test Model. Verification of coding parameters is done with Elecard HEVC Analyzer [7]. For AVC estimation JM reference encoder and Elecard StreamEye [7] are used. Both JM and HM utilize rate-distortion optimization (RDO) techniques to achieve quasi-optimal correlation between compression rate and quality. Both encoder implementations are evaluated in “constant quantizer” mode.
Estimation of VP9 performance is carried out with the VPX encoder from The WebM Project as it is the only implementation of this standard. CodecVisa VP9 Analyzer [8] is used for verification of compression parameters. VPX encoder is configured with “constrained quality” mode and limited quantization parameter to emulate “constant quantizer” mode.
Daala is still under development and the only encoder implementation available belongs to Xiph open source community, which is, in fact, developing this standard. Verification of compression parameters is performed manually as no analyzer is available. Only 'constrained quality' mode is available and used in experiments, which, by the way, should provide superior efficiency to “constant quantizer” mode.

Experiments are carried out on JCT-VC video sequences:  BasketballDrill (832×480 @ 50 Hz), Cactus (1920×1080 @ 50 Hz) and Traffic (2560×1600 @ 30 Hz) [9].

For key-frame compression efficiency estimation HM encoder is tested in “All Intra – Main” configuration, JM encoder is tested in “Intra HE” configuration. VP9 and Daala encoders are configured manually.


Fig. 3. Intra-frame compression efficiency on BasketballDrill sequence 

Fig. 4. Intra-frame compression efficiency on Cactus sequence 


Fig. 5. Intra-frame compression efficiency on Traffic sequence

Fig. 4. Inter-frame compression efficiency on BasketballDrill sequence

For inter-frame compression efficiency estimation HM encoder is tested in “Low-delay B – Main” configuration, JM encoder is tested in “Random Access B HE” configuration. VP9 and Daala encoders are configured manually. Key frame is set to be only the first in the coded sequence.

Fig. 5. Inter-frame compression efficiency on Cactus

Fig. 6. Inter-frame compression efficiency on Traffic

Conclusion

Experimental results obviously show that Daala video encoder is still rather far from being competitive. While HM provides 31% better compression rates in key-frame only mode and about 40% improvement in inter-coding mode compared to JM, VP9 is only 18% better than JM in both modes. It is worth mentioning that VP9 encoder doesn’t have great RDO model, so the VP9 standard itself may potentially have better performance.

References


1. Cisco Visual Networking Index: Global Mobile Data Traffic Forecast Update, 2012–2017. White paper. – Cisco, February 2013.
2. Recommendation H.264: Advanced video coding for generic audiovisual services. - ITU, June 2011.
3. Recommendation H.265: High efficiency video coding. - ITU, April 2013.
4. Ponomarev O.G., Sharabayko M.P., Posdnyakov A.A. Analiz effektivnosty metodov i algoritmov videokompressii standarta H.265/HEVC // Elektrosvyaz. – 2013 – №. 3. – pp. 29-33 (in Russian).
5. The WebM Project VP9 Video Codec. – URL: http://www.webmproject.org/vp9/ (14.10.2013).
6. Xiph.org Daala video. – URL: https://xiph.org/daala/ (14.10.2013).
7. Elecard Video analysis products. – URL: http://www.elecard.com/en/products/professional/analysis
8. CodecVisa Cloud. – URL: http://codecvisa.codecian.com/ (14.10.2013).
9. JCT-VC test sequences. – URL: ftp://ftp.tnt.uni-hannover.de/testsequences (14.10.2013).

See Also


17 comments:

  1. Thanks for conducting the tests. Wold you mind sharing the following information about how VP9 was run?
    In particular, what was the hash or at least the rough date of the code that was used? and more importantly, what the command-line was ?

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    1. VP9 encoder version v1.2.0-4614-gc5e9108 was run with:
      --min-q=%Q% --max-q=%Q% --kf-min-dist=%KF_DIST% --kf-max-dist=%KF_DIST% --passes=1
      where %Q% - is a quantization value, %KF_DIST% - key frame distance value

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  2. For 'constant quality' encoding, a better option is to run with:
    --end-usage=3 --cq-level=%Q% --kf-min-dist=%KF_DIST% --kf-max-dist=%KF_DIST% ...
    Also, currently the 1-pass encoding option in libvpx is kind of broken. So it is better to test with 2 passes for now - even though I agree that makes a fair comparison with the HM difficult.

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    Replies
    1. This is true for constant quality, but the tests were held in constant quantization mode. I consider this more fair comparison.

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    2. The "constant quality" mode (end-usage=3) in VP9 ensures that all regular INTER frames use the quantizer Q specified in the cq-level=Q parameter. The key frames and alt-ref frames however will use lower quantizer (higher quality).
      On the other hand, making max-q = min-q = Q, will make all frames have the same Q, which is not the best in coding performance. Just wanted to clarify in case there is any confusion.

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    3. Incase I am comparing a particular sequence for intra-frame comparison of HEVC and VP9, The Quantisation parameter will have to be set to a value same as in HEVC. In such a case do you suggest me to use max-q min-q =Q?? what would be the best usage in case of Intra frame comaprison.. Could you please help me with this?

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    4. Well, Shruti, there are at least two ays to compare pure encoder performance without rate control etc. One is to compare in constant quantization mode, another is - in constant quality mode. I prefer the first one as more simple, involving less decision-making algorithms.
      So yeah, I suggest max-q=min-q=Q

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  3. Hi Debargah, I am unable to follow HEVC standard even after reading documents. Can you provide me any source with good Explanation. Thanks

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    Replies
    1. http://iphome.hhi.de/wiegand/assets/pdfs/2012_12_IEEE-HEVC-Overview.pdf

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  4. Hi I'm trying to download the test sequences and they keep asking for a username and a password. Any idea where to get that?

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  5. Hello.
    Try the following link: ftp://hvc:US88Hula@ftp.tnt.uni-hannover.de/testsequences

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  6. That still asks for a username and a password.

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  7. This comment has been removed by a blog administrator.

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  8. Replies
    1. In the "See Also" section I sahre a link on such comparisson to x264. Though I think it's not a valid comparisson prejudiced.
      Anyway do you suggest that x264 in constant quantizer or constant quality mode would outperform JM?

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  9. Your comparison is based on PSNR values, something which Daala doesn't target as a performance factor.
    Actual perception is what Daala is targeting at.

    ReplyDelete
    Replies
    1. Raul,
      As far as I know there is no human psycho-visual perception model so far. Therefore neither SSIM, nor PSNR can be considered good distortion metric: there is just no criterion of truth.
      However I do agree that to be confident in RD-performance results, VQM or SSIM should be used also. I guess I'll update the comparison later on, but don't believe the results would change.

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