SVT -AV1向何处去
Moscow State University (MSU) issues multiple codec reports each year. 我觉得这些报告很可信，因为他们使用 very diverse content and realistic encoding parameters that the university derives in consultation with the codec developers. 我写了关于2020年报告的文章 go2sm.com/moscow2020.
其中一个非常值得注意的观察 报告是一贯惨淡的表现 of 基于可扩展视频技术(SVT)的编解码器. 在“MSU视频编解码器”中进行1 fps测试 对比2020第1部分:全高清，目标” report, SVT -HEVC and SVT -VP9 placed well behind x265 and WebM’s VP9; they’re even behind x264编解码器被设计用来取代. SVT -AV1 was four percentage points behind the Alliance for Open Media’s (AOMedia) libaom and 25 percentage points behind Visionular’s Aurora1 codec. 当然，SVT更重要 性能比质量更重要，但SVT -HEVC and SVT -VP9 trailed x264 and x265 again in 30-fps tests. (VP9 and Aurora didn’t make the performance cut.)
These results are most interesting as they relate to SVT -AV1, AO-Media已经全力投入的AV1编解码器. 具体地说, 2020年8月, AOMedia formed a software working group to leverage SVT -AV1 to “create AV1 encoder implementations that deliver excellent video compression across applications in ways that remove computational complexity trade-offs for an ever-growing video delivery marketplace.“这才过了大约一年, 所以很难批评这些努力, but the laggard performance of the SVT -based VP9 and HEVC codecs raises questions as to whether AOMedia chose the right architecture for AV1’s continued advancement.
我向大卫·隆卡提出了这些问题, Facebook’s director of video encoding and the former director of encoding technologies at Netflix. 他回答说, “据我所知, SVT -HEVC and SVT -VP9 were designed for live encoding, 并且对于其他用例并不真正有用. The threading performance is nearly linear, which means more cores = much faster encodes. Other codecs are not as efficient with many threads. SVT -AV1 performs very favorably to libaom, and delivers solid gains all 进入x264计算复杂度的方法. We (the SVT community) feel very good about SVT -AV1, and are continuing to invest in it. 它是设计最精良的编码器之一.”
关于编解码器的一般比较， Ronca added, “Intel shared a codec comparison at SPIE that is how modern codecs should be evaluated. The fundamental metric is per-shot, single-threaded, complexity vs. 效率.Ronca指的是一份名为"The SVT -AV1 Encoder: Overview, 特性 and Speed-Quality Tradeoffs,” which compared SVT -AV1 to libaom, x264, x265, and libvpx (VP9). The paper was published 2020年8月 and will cost you $21 to download. Or, you can check out Ronca making the key points in a video interview with John Porterfield on YouTube (go2sm.com/av1ronca; about 25 minutes in).
The testing for the paper was extensive, well-documented, and well-presented, although a 在我看来，触摸是特殊的 questions as to how the results will translate to 现实世界的应用程序. 例如, the researchers performed all encodes using constant rate factor encoding, which is very frequently used for academic codec comparisons, 但很少用于实际生产. 当我为我的文章测试AV1编码器时AV1 Has Arrived: Comparing Codecs From AOMedia, Visionular, and Intel/Netflix，“我使用双通道编码测试了SVT -AV1. Intel objected, saying that two-pass rate control had not yet been completed. 正如我在文章中解释的那样, I left SVT -AV1 in because I had already invested substantial time working with the codec and because it was freely available on GitHub without any warnings about two-pass performance. The white paper also didn’t test the Aurora1 codec, which performed best in my tests.
我向Ronca询问了这些问题, 他回应道, “If I was going to deploy AV1 and my use-case was 2-pass, 固定的共和党, 我可能想测试libvpx, SVT -AV1, and maybe some closed source AV1 encoders in 2-pass mode with 固定的共和党.”
白皮书总结道, “Preliminary experimental data with respect to faster presets show great promise that SVT -AV1 will eventually be the encoder of choice for a very-wide range of [video-on-demand] applications.“那 可能是这样吗, but I’m reminded that all codec comparisons are academic until they test your content with your encoder using your encoding parameters. The closer they are to your encoding schema, the more accurate they are likely to be.
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