Repository: yt-dlp
Issue: Unable to record YouTube livestreams while --embed-subs is set
Labels: docs/meta/cleanup,enhancement,triage,site:youtube,core:downloader

### DO NOT REMOVE OR SKIP THE ISSUE TEMPLATE

- [X] I understand that I will be **blocked** if I *intentionally* remove or skip any mandatory\* field

### Checklist

- [X] I'm requesting a site-specific feature
- [X] I've verified that I'm running yt-dlp version **2023.03.04** ([update instructions](https://github.com/yt-dlp/yt-dlp#update)) or later (specify commit)
- [X] I've checked that all provided URLs are playable in a browser with the same IP and same login details
- [X] I've searched [known issues](https://github.com/yt-dlp/yt-dlp/issues/3766) and 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.youtube.com/watch?v=jfKfPfyJRdk

### Provide a description that is worded well enough to be understood

I often want subtitles (if they are available) embedded into the output file, so I decided to add `--embed-subs` to yt-dlp's config file to automate this.

Unfortunately, this comes with a side effect: Unless explicitly overwritten with `--no-embed-subs`I'm unable to record/download YouTube livestreams or premieres, ass yt-dlp tries to download the live chat before capturing the video. Since, obviously, new chat messages will drop in every second, yt-dlp never starts actually recording recording.

yt-dlp also tells that
```
WARNING: Live chat download runs until the livestream ends. If you wish to download the video simultaneously, run a separate yt-dlp instance
```
so it's more a enhancement request than a bug report, but I don't see how this outcome is expected or intended.

So, while I get that this is partly my fault by adding `--embed-subs` to the config, I'd suggest to either handle the live chat not as subtitles at all (because they aren't), or at least record them simultaneously with the video.

### Provide verbose output that clearly demonstrates the problem

- [X] Run **your** yt-dlp command with **-vU** flag added (`yt-dlp -vU <your command line>`)
- [ ] If using API, add `'verbose': True` to `YoutubeDL` params instead
- [X] Copy the WHOLE output (starting with `[debug] Command-line config`) and insert it below

### Complete Verbose Output

```shell
[debug] Command-line config: ['-vU', 'https://www.youtube.com/watch?v=jfKfPfyJRdk']
[debug] User config "/Users/xxx/.config/yt-dlp/config": ['--force-ipv4', '--format', 'bestvideo[vcodec^=avc1]+bestaudio[ext=m4a]/bestvideo+bestaudio/best', '--embed-chapters', '--embed-subs', '--embed-metadata', '--fixup', 'never']
[debug] Encodings: locale UTF-8, fs utf-8, pref UTF-8, out utf-8, error utf-8, screen utf-8
[debug] yt-dlp version nightly@2023.06.17.224306 [01aba2519] (zip)
[debug] Python 3.11.4 (CPython arm64 64bit) - macOS-13.4-arm64-arm-64bit (OpenSSL 1.1.1u  30 May 2023)
[debug] exe versions: ffmpeg N-110783-g29710dd7f2 (setts), ffprobe N-110783-g29710dd7f2, phantomjs 2.1.1
[debug] Optional libraries: certifi-2023.05.07, pycrypto-3.17, sqlite3-2.6.0, websockets-11.0.3
[debug] Proxy map: {}
[debug] Loaded 1845 extractors
[debug] Fetching release info: https://api.github.com/repos/yt-dlp/yt-dlp-nightly-builds/releases/latest
Available version: nightly@2023.06.17.224306, Current version: nightly@2023.06.17.224306
Current Build Hash: 6774b889af8aec948511256bde94834063bb4729ea1e0a89a5b79e38a71e3593
yt-dlp is up to date (nightly@2023.06.17.224306)
[youtube] Extracting URL: https://www.youtube.com/watch?v=jfKfPfyJRdk
[youtube] jfKfPfyJRdk: Downloading webpage
[youtube] jfKfPfyJRdk: Downloading android player API JSON
[youtube] jfKfPfyJRdk: Downloading m3u8 information
[youtube] jfKfPfyJRdk: Downloading m3u8 information
[info] jfKfPfyJRdk: Downloading subtitles: live_chat
[debug] Sort order given by extractor: quality, res, fps, hdr:12, source, vcodec:vp9.2, channels, acodec, lang, proto
[debug] Formats sorted by: hasvid, ie_pref, quality, res, fps, hdr:12(7), source, vcodec:vp9.2(10), channels, acodec, lang, proto, filesize, fs_approx, tbr, vbr, abr, asr, vext, aext, hasaud, id
[info] jfKfPfyJRdk: Downloading 1 format(s): 96
[info] Writing video subtitles to: lofi hip hop radio 📚 - beats to relax⧸study to 2023-06-18 15_43 [jfKfPfyJRdk].live_chat.json
[debug] Invoking youtube_live_chat downloader on "https://www.youtube.com/watch?v=jfKfPfyJRdk&bpctr=9999999999&has_verified=1"
[youtube_live_chat] Downloading live chat
WARNING: Live chat download runs until the livestream ends. If you wish to download the video simultaneously, run a separate yt-dlp instance
[youtube_live_chat] Total fragments: unknown (live)
[download] Destination: lofi hip hop radio 📚 - beats to relax⧸study to 2023-06-18 15_43 [jfKfPfyJRdk].live_chat.json
[download]    1.39MiB at  931.54KiB/s (00:00:00) (frag 2)
```