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Netflix Finds VP9 Offers Strong Compression At 1080p, Approaches HEVC Performance

Netflix, being one of the biggest video streaming services in the world, tested how efficient various video codecs are for a given level of quality. The company discovered that the royalty-free VP9 codec developed primarily by Google is almost as efficient as HEVC, and can sometimes be even better at resolutions of 1080p and higher.

Netflix has over 83 million subscribers who watch billions of hours of TV shows and movies, according to the company. The service was made available in over 130 countries this year, which means it could potentially grow much larger in the future, once more people discover it and have the requisite internet access. More people are using it over cellular networks as well, which makes delivering the video streams as efficiently as possible a high priority for Netflix.

Testing h.264, HEVC, VP9

The company evaluated the three (currently) most popular video codecs: h.264/AVC (still the most popular one by far); the next-generation h.265/HEVC; and Google’s royalty-free competitor, VP9. The company used open source encoders for all three, including x264 for h.264 videos, x265 for HEVC videos, and libvpx for VP9 videos.

Both HEVC and VP9 promise about 50% bitrate savings for the same quality compared to h.264, but Netflix wanted to test for itself to see if this is true. Netflix sampled 5,000 12-second clips from its catalog, which includes a wide range of genres and signal characteristics.

With three codecs, two configurations, three resolutions (480p, 720p and 1080p), and eight quality levels per configuration-resolution pair, the company had more than 200 million encoded frames. Netflix applied six quality metrics: PSNR, PSNRMSE, SSIM, MS-SSIM, VIF and VMAF. This resulted in more than half a million bitrate-quality curves. Netflix’s unused cloud-based encoding infrastructure allowed the company to complete this large test in only a few weeks.

Test Results

The company learned that previous research showing up to 50% bitrate savings for both HEVC and VP9 compared to h.264 turned out to be true. HEVC’s x265 implementation outperformed VP9’s libvpx for most resolutions and quality metrics. However, at the 1080p resolution, the difference was either much smaller (in HEVC’s favor), or, in some cases, VP9 even beat HEVC in bitrate savings.

The fact that VP9 performs better at 1080p or higher is not a major surprise, considering VP9 was optimized for resolutions beyond HD. Google is currently using it for YouTube, where all videos are encoded in VP9.

Codec Adoption

VP9’s predecessor, the VP8 codec, failed to gain traction because it arrived much later than h.264, and because chip makers weren’t too interested in utilizing hardware accelerators for it. This has changed somewhat with VP9, as more and more chips come out with accelerated decoding, and even encoding, for VP9.

However, by the time either VP9 or HEVC become too ubiquitous, a new generation of royalty-free video codecs that are being standardized by the IETF may arrive to replace both. Google, as well as Mozilla, Cisco, Intel, Microsoft, and even Netflix itself are all contributing designs, code, and patents to create a new standard royalty-free codec that everyone can use.

Update, 8/30/16, 2:17pm PT: It's come to our attention that the original headline in this article was poorly worded to the point of being misleading. We have replaced it with a different headline.

  • DocBones
    Wonder why they didnt do 4k testing.
    Reply
  • I'm guessing 4k testing wasn't done because of lack of samples, time and resources (spare cloud processing). I really wouldn't be surprised if it was in the works. I'm more and more impressed by Netflix, seems like they are really improving.
    Reply
  • bit_user
    We'll see how long it stays royalty-free. Patent trolls might find something it infringes. Compression is such a patent minefield that it's hard to do anything (good) with no risk of infringement.

    BTW, I don't know why they even bothered with PSNR or PSNRMSE. I hope those didn't skew the results.
    Reply
  • RomeoReject
    Does this mean there's any hope of them ditching Silverlight? I find it a bit frustrating that my mid-range gaming computer can only do stereo and 720p, yet my far weaker phone could inexplicably do 5.1 and 1080p because it uses the app instead.
    Reply
  • alextheblue
    So VP9 is *sometimes* better. The headline made it sound like they'd made some breakthrough, because at most resolutions and content HEVC wins even with the x265 open source encoder. Given how long it took for it's open source predecessor x264 to catch up to commercial encoders, I would imagine there's pay solutions that produce even better results, further distancing HEVC from VP9 in commercial encodes. For most purposes though VP9 is still good enough.

    18517786 said:
    Does this mean there's any hope of them ditching Silverlight? I find it a bit frustrating that my mid-range gaming computer can only do stereo and 720p, yet my far weaker phone could inexplicably do 5.1 and 1080p because it uses the app instead.

    Well if you run Windows 10 you just download the Netflix app and everything works perfectly at any resolution, even UHD where content exists for 4k. Problem solved.
    Reply
  • BobKatopolis
    You took Netflix's blog post, which explained that x265 outperformed VP9 under most circumstances, and wrote an article with a clickbait title that says exactly the opposite. Nicely done.
    Reply
  • Shevach
    Not all researchers agree with the statement that VP9 and HEVC are comparable.
    For example, the results reported in the paper "Contemporary Video Compression Standards H.265/HEVC, VP9, VP10, Daala" by M.P. Sharabayko, N.G. Markov reveals that HEVC is still superior to VP9.
    Reply
  • Shevach
    Not all researches agree with the statement that VP9 is comparable to HEVC.
    For example in the paper "Contemporary Video Compression Standards
    H.265/HEVC, VP9, VP10, Daala" (by M.P. Sharabayko, N.G. Markov, 2016) reported that HEVC is still superior to VP9.
    Reply
  • dark_lord69
    18517786 said:
    Does this mean there's any hope of them ditching Silverlight? I find it a bit frustrating that my mid-range gaming computer can only do stereo and 720p, yet my far weaker phone could inexplicably do 5.1 and 1080p because it uses the app instead.

    It's not your computer's fault...
    "5.1 surround sound is not currently supported while streaming on a computer using Microsoft Silverlight or HTML5."

    "The HTML5 Player may limit the quality of the stream while the Silverlight player does not. HD resolution streams are only available if the Internet connection supports at least 5 Megabits per second, but that is not the only restriction."

    As for the 1080p resolution you could probably blame that on your ISP, not your computer.
    Reply
  • CrssdOut
    i gotta agree, i know 4k is still a small growing market, but to skip that testing?
    Reply