Disclosure: I work at TPStreams, a video hosting and streaming platform. This post explains the general technique, which applies whichever provider (or none) you use.

If you've ever put an MP4 behind a <video> tag and watched it stall on a phone over 4G, you've hit the problem adaptive bitrate (ABR) streaming solves. Here's how it works with HLS, the format you'll meet most often.

The problem with a single file

A single MP4 has one resolution and one bitrate. Encode it at 1080p and 5 Mbps and viewers on slow connections buffer; encode it at 480p and everyone on fibre gets a blurry picture.…