Downloading subtitle no longer works for any Youtube video - WARNING: Unable to download subtitle: unknown url type:

[heavenhunter]

Checklist

• I'm reporting a broken site support
• I've verified that I'm running youtube-dl version 2025.01.01
• I've checked that all provided URLs are alive and playable in a browser
• I've checked that all URLs and arguments with special characters are properly quoted or escaped
• I've searched the bugtracker for similar issues including closed ones

Verbose log

[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['--ignore-config', '-v', '--skip-download', '--write-sub', '--all-subs', 'https://www.youtube.com/watch?v=Z8CV-d_fYb8']
[debug] Encodings: locale cp1252, fs utf-8, out utf-8, pref cp1252
[debug] youtube-dl version 2025.01.01 [176fc2cb0]
[debug] ** This version was built from the latest master code at https://github.com/ytdl-org/youtube-dl.
[debug] ** For support, visit the main site.
[debug] Python 3.9.2 (CPython AMD64 64bit) - Windows-10-10.0.19041-SP0 - OpenSSL 1.1.1i  8 Dec 2020
[debug] exe versions: ffmpeg 4.3.1, ffprobe 4.3.1, phantomjs 2.1.1
[debug] Proxy map: {}
[youtube] Z8CV-d_fYb8: Downloading webpage
[youtube] Z8CV-d_fYb8: Downloading API JSON
[debug] [youtube] Decrypted nsig 6ftmofEWFduToWC6- => mZaRqiK3m7r8rA
[debug] [youtube] Decrypted nsig f1i0ZwuVRzwvA2RHW => 5GnAXA82_gb58g
[debug] Default format spec: bestvideo+bestaudio/best
[info] Writing video subtitles to: How to find Creative Commons Videos on YouTube (without copyrights claim)-Z8CV-d_fYb8.en.vtt
WARNING: Unable to download subtitle for "en": unknown url type: '/api/timedtext?v=Z8CV-d_fYb8&ei=-a54Z4f_Fc7BssUPperpqQ8&caps=asr&opi=112496729&xoaf=5&hl=en&ip=0.0.0.0&ipbits=0&expire=1735987561&sparams=ip%2Cipbits%2Cexpire%2Cv%2Cei%2Ccaps%2Copi%2Cxoaf&signature=598FDC77A3FE2FA972CD474EDC7A37B931C1482E.6747BA7531C1291708DD03624CE08CAB3CC382CA&key=yt8&lang=en&fmt=vtt'

Description

Downloading subtitle no longer works for any Youtube video. Example =

youtube-dl --ignore-config -v --skip-download --write-sub --all-subs https://www.youtube.com/watch?v=Z8CV-d_fYb8

The last time I saw this worked correctly was on 26 November 2024.
After that, on 22 December 2024, I updated youtube-dl to version 2024.12.17 and started to see this error.
Today, tried updating to version 2025.01.01 but the error still occurs.

[dirkf]

I expect this is a side-effect of the emergency switch to the MWEB API, where the subtitles might be found in a different place or maybe not supplied. Let's see if we can find them again.

[dirkf]

Although the subtitle data is where it was expected, the URLs are just paths that need to be completed with scheme://host (which wasn't the case with the previous source). Then, with the problem video, we get the one non-automatic subtitle:

$ python -m youtube_dl -v --skip-download --write-sub --all-subs 'https://www.youtube.com/watch?v=Z8CV-d_fYb8'
[debug] System config: [u'--prefer-ffmpeg']
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: [u'-v', u'--skip-download', u'--write-sub', u'--all-subs', u'https://www.youtube.com/watch?v=Z8CV-d_fYb8']
[debug] Encodings: locale UTF-8, fs UTF-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2021.12.17
[debug] Git HEAD: 176fc2cb0
[debug] Python 2.7.18 (CPython i686 32bit) - Linux-4.4.0-210-generic-i686-with-Ubuntu-16.04-xenial - OpenSSL 1.1.1w  11 Sep 2023 - glibc 2.15
[debug] exe versions: avconv 4.3, avprobe 4.3, ffmpeg 4.3, ffprobe 4.3
[debug] Proxy map: {}
[youtube] Z8CV-d_fYb8: Downloading webpage
[youtube] Z8CV-d_fYb8: Downloading API JSON
[debug] [youtube] Decrypted nsig 5BrwAiPglXFWk1PRG => X09r8mo0vTdhCA
[debug] [youtube] Decrypted nsig U-fxiwVl1eHFyt6CP => c4MgdYO16CoNuA
[debug] Default format spec: bestvideo+bestaudio/best
[info] Writing video subtitles to: How to find Creative Commons Videos on YouTube (without copyrights claim)-Z8CV-d_fYb8.en.vtt
$