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

转发一篇x264, x265和 libvpx比较的文章, h265比h264码率到底能降低多少，相信很多人都听说265码率低了很多，实际应用场景到底如何，还是需要验证的，这篇文章作者筛选了5000个时长12秒的视频，做了实际的测试，转发一下， 原文出处请点击 ，如有版权问题，请联系我删除. 

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.

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