以渐进的方式对待过去

The year is 2023, but the type of files that most video transcode systems output hasn’t appreciably changed since Obama was president, despite most playback not occurring on those types. Among the most promising remedies to the problem was widely believed to be technically impractical, until we here at Vimeo got our hands on it. This article explains the origins of Artax, our solution for legacy progressive video on the fly.

今年是 2023 年，但自奥巴马担任总统以来，大多数视频转码系统输出的文件类型并没有发生明显变化，尽管大多数回放并不发生在这些类型上。人们普遍认为最有希望解决这一问题的方法在技术上是不切实际的，直到我们 Vimeo 开始着手研究。这篇文章介绍了 Artax 的起源，它是我们为传统渐进式视频提供的解决方案。

Some history

一些历史

Adaptive Bitrate streaming, or ABR, has been the industry standard for video playback on the Internet for almost a decade now. Pretty much every player and device you’ll come across supports it. It’s great — you no longer need to sit and buffer enough until playback is possible; the player can choose resolutions and bitrates for playback to give you the best experience possible.

近十年来，自适应码率流或 ABR 已成为互联网视频播放的行业标准。几乎所有的播放器和设备都支持它。这很好--你不再需要坐着缓冲到可以播放为止；播放器可以为播放选择分辨率和比特率，尽可能为你提供最佳体验。

The standard way ABR is served is via Common Media Application Format, or CMAF, fragments, which is based on fragmented ISOBMFF — that’s ISO Base Media File Format, better known as MP4 — with audio and video tracks stored as separate files. These files are fragmented, in our case at six-second intervals, which means that every six-second fragment can be used as a switching point in playback software to change resolution, bitrate, and so on. Both HLS and MPEG-DASH support CMAF, as do almost all players that use their own manifest format.

提供 ABR 的标准方式是通过通用媒体应用格式（或称 CMAF）片段，它基于片段ISOBMFF（即 ISO 基本媒体文件格式，又称 MP4），音轨和视频轨存储为单独的文件。这些文件被分割成片段，在我们的例子中，每隔六秒分割一次，这意味着每六秒的片段可以作为播放软件的切换点，以改变分辨率、比特率等。HLS和MPEG-DASH都支持 CMAF，几乎所有使用自己清单格式的播放器都支持 CMAF。

Given this, our current transcode stack naturally outputs transcodes in this format, and we store them this way, rather than progressive ISOBMFF, which is the sort where all of the audio and video data is put at the back (or...