Repository: yt-dlp
Issue: Unable to download multiple subtitles of same language
Labels: enhancement

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## Checklist

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- Make sure that all provided video/audio/playlist URLs (if any) are alive and playable in a browser.
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- [x] I'm reporting a bug unrelated to a specific site
- [x] I've verified that I'm running yt-dlp version **2021.09.02**
- [ ] I've checked that all provided URLs are alive and playable in a browser
- [ ] The provided URLs do not contain any DRM to the best of my knowledge
- [ ] I've checked that all URLs and arguments with special characters are properly quoted or escaped
- [x] I've searched the bugtracker for similar bug reports including closed ones
- [x] I've read bugs section in FAQ


## Verbose log

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Provide the complete verbose output of yt-dlp that clearly demonstrates the problem.
Add the `-v` flag to your command line you run yt-dlp with (`yt-dlp -v <your command line>`), copy the WHOLE output and insert it below. It should look similar to this:
 [debug] System config: []
 [debug] User config: []
 [debug] Command-line args: [u'-v', u'http://www.youtube.com/watch?v=BaW_jenozKc']
 [debug] Encodings: locale cp1251, fs mbcs, out cp866, pref cp1251
 [debug] yt-dlp version 2021.09.02
 [debug] Python version 2.7.11 - Windows-2003Server-5.2.3790-SP2
 [debug] exe versions: ffmpeg N-75573-g1d0487f, ffprobe N-75573-g1d0487f, rtmpdump 2.4
 [debug] Proxy map: {}
 <more lines>
-->

```
yt-dlp -v --list-subs https://cmaf.lln.latam.hbomaxcdn.com/videos/GYPGKMQjoDkVLBQEAAAAo/1/1b5ad5/1_single_J8sExA_1080hi.mpd
[debug] Command-line config: ['-v', '--list-subs', 'https://cmaf.lln.latam.hbomaxcdn.com/videos/GYPGKMQjoDkVLBQEAAAAo/1/1b5ad5/1_single_J8sExA_1080hi.mpd']
[debug] Encodings: locale cp1252, fs utf-8, out utf-8, pref cp1252
[debug] yt-dlp version 2021.09.02 (exe)
[debug] Python version 3.8.10 (CPython 64bit) - Windows-8.1-6.3.9600-SP0
[debug] exe versions: ffmpeg 2021-06-23-git-947122f111-full_build-www.gyan.dev, ffprobe 2021-06-23-git-947122f111full_build-www.gyan.dev
[debug] Optional libraries: mutagen, pycryptodome, sqlite, websockets
[debug] Proxy map: {}
[debug] [generic] Extracting URL: https://cmaf.lln.latam.hbomaxcdn.com/videos/GYPGKMQjoDkVLBQEAAAAo/1/1b5ad5/1_single_J8sExA_1080hi.mpd
[generic] 1_single_J8sExA_1080hi: Requesting header
WARNING: [generic] Falling back on generic information extractor.
[generic] 1_single_J8sExA_1080hi: Downloading webpage
[generic] 1_single_J8sExA_1080hi: Extracting information
[debug] Formats sorted by: hasvid, ie_pref, lang, quality, res, fps, vcodec:vp9.2(10), acodec, filesize, fs_approx, tbr, vbr, abr, asr, proto, vext, aext, hasaud, source, id
Available subtitles for 1_single_J8sExA_1080hi:
Language Formats
en-US    vtt
es-419   vtt, vtt
pt-BR    vtt, vtt
```
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## Description

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Hi. I have been trying to download a webtt subtitle from `H*O M*X`. When I run the command posted in verbose log, yt-dlp shows that there's two availables subtitles in spanish (complete and forced) but it only downloads one.

**ffmpeg** also shows that every subtitle has their own ID, but it can't download any of them because of... you know.

```
    Side data:
      unknown side data type 24 (842 bytes)
  Stream #0:30(en-US): Subtitle: webvtt
    Metadata:
      id              : t2
  Stream #0:31(es-419): Subtitle: webvtt
    Metadata:
      id              : t8
  Stream #0:32(es-419): Subtitle: webvtt
    Metadata:
      id              : t4
  Stream #0:33(pt-BR): Subtitle: webvtt
    Metadata:
      id              : t0
  Stream #0:34(pt-BR): Subtitle: webvtt
    Metadata:
      id              : t6
```

I've used the following commands, but the result is always the same:

`yt-dlp --skip-download --allow-unplayable-formats --write-subs --sub-langs es-419 --sub-format vtt "https://cmaf.lln.latam.hbomaxcdn.com/videos/GYPGKMQjoDkVLBQEAAAAo/1/1b5ad5/1_single_J8sExA_1080hi.mpd"`

`yt-dlp --skip-download --allow-unplayable-formats --write-subs --sub-langs all --sub-format vtt "https://cmaf.lln.latam.hbomaxcdn.com/videos/GYPGKMQjoDkVLBQEAAAAo/1/1b5ad5/1_single_J8sExA_1080hi.mpd"`

I need to download the second one. Any suggestion?