If you try watching a video recording on twitch etc. while it’s still ‘live’, mpv/youtube-dl will play the live video instead of starting from the beginning.

The fix is straightforward: By appending ?t=0m you can force it to start at the beginning:

mpv 'https://www.twitch.tv/example/v/12345?t=0'

This is also useful for a second purpose: seeking. Normally, by trying to seek a live stream like this in mpv you will end up buffering and downloading forever. (I’m not exactly sure what’s going on since the mpv cache is so opaque, but I have to imagine it’s actually trying to download all the data you skipped past)

By changing it to e.g. ?t=20m you can seek to 20 minutes in the stream.