When it Comes to Bitrates, Less is Always 更多的

M大多数流媒体专业人士都知道这一点 bandwidth usage has spiked as millions of workers are furloughed or working 由于COVID-19，我不能在家. What can streaming producers do in 的 short term to reduce 的 load?

网飞公司首先加入删除的 highest-bandwidth streams from its manifest files, so even if you had 的 bandwidth to retrieve that stream, 你的玩家不会知道它在那里. This is an option that all streaming producers should consider because it’s easy to implement and, unlike more drastic changes I will discuss later, 有很少的测试意义吗.

除此之外, 生产商应该考虑预处理, 某种形式的标题编码, 并部署新的编解码器, 按照这个顺序. By pre-processing, I mean using technologies like ZPEG or BitSave that pre-process your video 在转码. Your encoding and packaging pipeline should remain 的 same, but you should produce higher-quality files at lower bitrates with minimal compatibility risk during playback.

Next to consider is 某种形式的标题编码, if you haven’t done this already. (见 go2sm.com/scene for a review of 的 evolution of per-title technologies.每个标题有多种形式, such as Capped CRF you can implement yourself, Beamr逐帧优化, and features in cloud-based services like Bitmovin and Mux or products/services like AWS Elemental’s Quality-Defined Variable Bitrate (QVBR) encoding, 谐波的EyeQ, and Capella Systems’ Source Adaptive Bitrate Ladder. Note that AWS Elemental and Harmonic offer per-title for both video on demand and live.

Netflix dropped 的 top bitrate of its encoding ladder with minimal perceptible quality loss because it uses per-scene adaptation, 按标题编码的一种高级形式. Whereas a fixed ladder might always deploy a 1080p stream at 的 top quality followed by 720p, 的 most advanced forms of per-title might deploy two 1080p streams for some clips so 的 viewer still gets a 1080p stream if 的 top quality stream is dropped.

How much benefit you’ll get from per-title depends on 的 type of footage you stream and 的 data rates deployed in your current ladder. If you’re streaming soccer matches at a maximum data rate of 4.5Mbps, per-title encoding won’t deliver much savings. 然而, if you stream a range of content and your top quality 1080p stream is 8Mbps, you should see significant bandwidth reductions on many of your streams.

和下一个选项比较, 改变编解码器, per-title is fairly low risk because you’re still working with H.264. It’s also cheaper since you’re still only producing and distributing a single codec. Adding any codec to 的 mix increases encoding cost and storage cost, 降低缓存效率, and involves a development cost to ensure playback compatibility.

Bitrate savings depend on 的 codec and codec implementation. 根据莫斯科国立大学的11月. 1, 2019, “Video Codecs Comparison,” savings for HEVC and VP9 averaged around 40% compared to H.264, with 的 proprietary WZAurora AV1 Encoder delivering about 20% more efficiency than 的 highest-performing HEVC codec. This is roughly similar to 的 20% savings AV1 delivered over VP9 that Netflix announced earlier this year. 然而, encoding AV1 is still glacial, which translates to much higher encoding costs. 而AWS Elemental收费为0美元.每分钟1080p30小时.264编码和$0.048 per minute of HEVC, 的 price skyrockets to $0.864 per minute of AV1 encoding, a premium of 36x over H.264. This likely makes AV1 impractical for all but 的 highest-volume producers, 像Netflix, YouTube, Hulu, 脸谱网, 和亚马逊.

这些编解码器应该在哪里使用? HEVC should play seamlessly on most iOS devices with minimal muss or fuss, 以及OTT设备和智能电视. VP9应该在Chrome和 Firefox on all platforms, plus Android and most newer OTT devices and smart TVs.

What about 的 2020 crop of MPEG codecs—VVC, EVC, and LCEVC? The first two will require hardware support for playback and 的refore won’t really become relevant until 2022 or so. LCEVC is backward-compatible with existing H.264 and HEVC hardware playback and is implemented now by V-Nova as P+. 在提交给MPEG时， V-Nova声称 LCEVC提供的质量与H.264 at a bandwidth savings of 45%, making it a technology that could have an impact in 2020.

No one knows how long 的 COVID-19-related usage spikes will continue, but 的 situation presents a stark reminder of what we all knew all along: When it comes to streaming video, 少即是多. At 的 same or better visual quality, of course.

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Video: The Case for Custom Encoding, Part 1: Bitrate

Streaming Learning Center's 1月时 makes 的 case for custom, 每个标题编码在Netflix模型上, focusing on bitrate issues in part 1 of this 2-part series from his 流媒体 West presentation.

2017年2月2日