Repository: yt-dlp
Issue: Twitch subtitles extraction
Labels: site-enhancement

### Checklist

- [X] I'm reporting a site feature request
- [X] I've verified that I'm running yt-dlp version **2022.01.21**. ([update instructions](https://github.com/yt-dlp/yt-dlp#update))
- [X] I've checked that all provided URLs are alive and playable in a browser
- [X] I've searched the [bugtracker](https://github.com/yt-dlp/yt-dlp/issues?q=) for similar issues including closed ones. DO NOT post duplicates
- [X] I've read the [guidelines for opening an issue](https://github.com/yt-dlp/yt-dlp/blob/master/CONTRIBUTING.md#opening-an-issue)
- [ ] I've read about [sharing account credentials](https://github.com/yt-dlp/yt-dlp/blob/master/CONTRIBUTING.md#are-you-willing-to-share-account-details-if-needed) and I'm willing to share it if required

### Region

_No response_

### Example URLs

https://www.twitch.tv/videos/1283067527

### Description

Twitch provides subtitles for some livestreams and VODs, which aren't downloaded with yt-dlp.
AFAIK the subtitles can be both pre-made and auto-generated (like the example link), 
The subtitles seem to be auto generated on the spot every time.

### Verbose log

```shell
yt-dlp --write-subs --write-auto-subs --sub-langs all -v https://www.twitch.tv/videos/1283067527
[debug] Command-line config: ['--write-subs', '--write-auto-subs', '--sub-langs', 'all', '-v', 'https://www.twitch.tv/videos/1283067527']
[debug] Encodings: locale cp1252, fs utf-8, out utf-8, err utf-8, pref cp1252
[debug] yt-dlp version 2022.01.21 [f20d607] (win_dir)
[debug] Python version 3.8.10 (CPython 64bit) - Windows-10-10.0.19043-SP0
[debug] exe versions: ffmpeg N-105336-g7247a6fed8-20220122 (setts), ffprobe N-105336-g7247a6fed8-20220122
[debug] Optional libraries: Cryptodome, mutagen, sqlite, websockets
[debug] Proxy map: {}
[debug] [twitch:vod] Extracting URL: https://www.twitch.tv/videos/1283067527
[twitch:vod] 1283067527: Downloading stream metadata GraphQL
[twitch:vod] 1283067527: Downloading video access token GraphQL
[twitch:vod] 1283067527: Downloading m3u8 information
[debug] Formats sorted by: hasvid, ie_pref, lang, quality, res, fps, hdr:12(7), vcodec:vp9.2(10), acodec, filesize, fs_approx, tbr, vbr, abr, asr, proto, vext, aext, hasaud, source, id
[debug] Downloading subtitles: rechat
[debug] Default format spec: bestvideo*+bestaudio/best
[info] v1283067527: Downloading 1 format(s): 1080p60
[info] Writing video subtitles to: celeste for a future youtube video lol rest of the vod had to be trashed [v1283067527].rechat.json
[debug] Invoking downloader on "https://api.twitch.tv/v5/videos/1283067527/comments?client_id=kimne78kx3ncx6brgo4mv6wki5h1ko"
[download] Destination: celeste for a future youtube video lol rest of the vod had to be trashed [v1283067527].rechat.json
[download] 100% of 58.22KiB in 00:00
[debug] Invoking downloader on "https://d1m7jfoe9zdc1j.cloudfront.net/106e8c6642b14272d8c5_tanukidan_14773148319_1549911041/chunked/highlight-1283067527.m3u8"
[hlsnative] Downloading m3u8 manifest
[hlsnative] Total fragments: 513
[download] Destination: celeste for a future youtube video lol rest of the vod had to be trashed [v1283067527].mp4
[download] 100% of 2.63GiB in 04:38
[debug] ffprobe command line: ffprobe -hide_banner -show_format -show_streams -print_format json "file:celeste for a future youtube video lol rest of the vod had to be trashed [v1283067527].mp4"
[FixupM3u8] Fixing MPEG-TS in MP4 container of "celeste for a future youtube video lol rest of the vod had to be trashed [v1283067527].mp4"
[debug] ffmpeg command line: ffmpeg -y -loglevel "repeat+info" -i "file:celeste for a future youtube video lol rest of the vod had to be trashed [v1283067527].mp4" -map 0 -dn -ignore_unknown -c copy -f mp4 "-bsf:a" aac_adtstoasc -movflags "+faststart" "file:celeste for a future youtube video lol rest of the vod had to be trashed [v1283067527].temp.mp4"
```