A Large-Scale Comparison of x264, x265, and libvpx?—?a Sneak?Peek
by Jan De Cock, Aditya Mavlankar, Anush Moorthy, and Anne Aaron

?With 83+ million members watching billions of hours of TV shows and movies, Netflix sends a huge amount of video bits? ?through the Internet. As we grow globally, more of these video bits will be streamed through bandwidth-constrained cellular? ?networks. Our team works on improving our video compression efficiency to ensure that we are good stewards of the Internet? ?while at the same time delivering the best video quality to our members. Part of the effort is to evaluate the state-of-the-art? ?video codecs, and adopt them if they provide substantial compression gains.

?H.264/AVC is a very widely-used video compression standard on the Internet, with ubiquitous decoder support on web? ?browsers, TVs, mobile devices, and other consumer devices.?x264?is the most established open-source software encoder for? ?H.264/AVC. HEVC is the successor to H.264/AVC and results reported from standardization showed?about 50% bitrate? ?savings?for the same quality compared to H.264/AVC.?x265?is an open-source HEVC encoder, originally ported from the x264? ?codebase. Concurrent to HEVC, Google developed VP9 as a royalty-free video compression format and released?libvpx?as an? ?open-source software library for encoding VP9.?YouTube reported?that by encoding with VP9, they can deliver video at half the? ?bandwidth compared to legacy codecs.

?We ran a large-scale comparison of x264, x265 and libvpx to see for ourselves whether this 50% bandwidth improvement is? applicable to our use case. Most codec comparisons in the past focused on evaluating what can be achieved by the bitstream? syntax (using the reference software), applied settings that do not fully reflect our encoding scenario, or only covered a limited? set of videos. Our goal was to assess what can be achieved by encoding with practical codecs that can be deployed to a? production pipeline, on the Netflix catalog of movies and TV shows, with encoding parameters that are useful to a streaming? service. We sampled 5000 12-second clips from our catalog, covering a wide range of genres and signal characteristics. With 3? codecs, 2 configurations, 3 resolutions (480p, 720p and 1080p) and 8 quality levels per configuration-resolution pair, we? generated more than 200 million encoded frames. We applied six quality metrics?—?PSNR, PSNR(MSE), SSIM, MS-SSIM, VIF and?VMAF?—?resulting in more than half a million bitrate-quality curves. This encoding work required significant compute capacity. However, our?cloud-based encoding infrastructure, which?leverages unused Netflix-reserved AWS web servers dynamically, enabled us to complete the experiments in just a few weeks.

What did we?learn?
Here’s a snapshot: x265 and libvpx demonstrate superior compression performance compared to x264, with bitrate savings reaching up to 50% especially at the higher resolutions. x265 outperforms libvpx for almost all resolutions and quality metrics, but the performance gap narrows (or even reverses) at 1080p.

Want to know?more?
We will present our methodology and results this coming Wednesday, August 31, 8:00 am PDT at the SPIE Applications of Digital Image Processing conference,?Session 7: Royalty-free Video.?We will stream the whole session live on Periscope and YouTube:?follow Anne for notifications?or come back to this page for links to the live streams. This session will feature other interesting technical work from leaders in the field of Royalty-Free Video. We will also follow-up with a more detailed tech blog post and extend the results to include 4K encodes.

大牛直播SDK除了支持RTSP H.265播放和錄像，目前還實現了Windows/Android/iOS平臺RTMP H.265擴展播放/錄像/轉發，並提供了配套的服務器支撐，開發者需要測試，可以到https://github.com/daniulive/SmarterStreaming下載。

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h264, h265 和 libvpx 比較(h264/avc, hevc 和vp9比較)