[RFC] demux: add demuxer for YouTube's json3 timedtext subtitles

[ghost]

Implementation was AI-assisted, not vibecoded.

I've added a new demuxer to support youtube's "timedtext" subtitle format used for their auto-generated subtitles, with the option to display each word as it's spoken, or line by line like regular subtitles.

Also modified the ytdl_hook.lua to optionally return auto generated subtitles.

[afishhh]

I've added a new demuxer to support youtube's "timedtext" subtitle format used for their auto-generated subtitles

This isn't entirely unreasonable but you do realize that there is a perfectly functional SRV3 demuxer/renderer in mpv which also works for auto-generated subtitles, yes?

At the very least the JSON3 "demuxer" is a completely separate feature because YouTube's auto-generated subtitles can be downloaded in any of their supported formats, not only JSON3, and so would also work without it.

[ghost]

I've added a new demuxer to support youtube's "timedtext" subtitle format used for their auto-generated subtitles

This isn't entirely unreasonable but you do realize that there is a perfectly functional SRV3 demuxer/renderer in mpv which also works for auto-generated subtitles, yes?

At the very least the JSON3 "demuxer" is a completely separate feature because YouTube's auto-generated subtitles can be downloaded in any of their supported formats, not only JSON3, and so would also work without it.

No I wasn't aware of subrandr. I've never used a disto where it's been enabled and didn't see anyone mentioning it when searching about auto subs, my bad I should have double checked.

I've created #18477 for the ytdl hook changes that enable auto generated subs by default (in SRV3 for builds with subrandr).

I'm personally not sure if the json3 demuxer is worth merging. I think it does provide a better out of the box experience than default for people watching youtube with a non-subrandr build, but maybe it's unnecessary.