Repository: youtube-dl
Issue: youtube.com 404 error when downloading subtitle.
Labels: cant-reproduce

## Checklist

- [x] I'm reporting a broken site support
- [x] I've verified that I'm running youtube-dl version **2021.04.17**
- [x] I've checked that all provided URLs are alive and playable in a browser
- [x] I've checked that all URLs and arguments with special characters are properly quoted or escaped
- [x] I've searched the bugtracker for similar issues including closed ones

```
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['--socket-timeout', '60', '-i', '--no-call-home', '--restrict-filenames', '--no-playlist', '--hls-prefer-native', '-f', '22,20,18', '--write-auto-sub', '--write-description', '--user-agent', 'Mozilla/5.0 (Windows NT 10.0; WOW64; rv:56.0) Gecko/20100101 Firefox/56.0', '--cookies', '/mnt/md7/to-go-through/cookies.txt', '--verbose', 'https://www.youtube.com/watch?v=rXUafEqpTvU']
[debug] Encodings: locale ANSI_X3.4-1968, fs ascii, out ANSI_X3.4-1968, pref ANSI_X3.4-1968
[debug] youtube-dl version 2021.04.17
[debug] Python version 3.5.3 (CPython) - Linux-5.11.12-nopreempt-Radeon-SI-dav11-x86_64-with-debian-9
[debug] exe versions: ffmpeg 3.2.15-0, ffprobe 3.2.15-0, rtmpdump 2.4
[debug] Proxy map: {}
[youtube] rXUafEqpTvU: Downloading webpage
[youtube] Downloading just video rXUafEqpTvU because of --no-playlist
[youtube] rXUafEqpTvU: Downloading MPD manifest
[info] rXUafEqpTvU: downloading video in 2 formats
[info] Writing video description to: You_can_-j_REJECT_but_you_can_not_hide_-_Global_scanning_of_the_IPv6_Internet_33c3_-_deutsche_Ubers-rXUafEqpTvU.description
[info] Writing video subtitles to: You_can_-j_REJECT_but_you_can_not_hide_-_Global_scanning_of_the_IPv6_Internet_33c3_-_deutsche_Ubers-rXUafEqpTvU.en.vtt
WARNING: Unable to download subtitle for "en": Unable to download webpage: HTTP Error 404: Not Found (caused by <HTTPError 404: 'Not Found'>); please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; see  https://yt-dl.org/update  on how to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.
[debug] Invoking downloader on 'https://r3---sn-5uaeznde.googlevideo.com/videoplayback?expire=1618867984&ei=sKJ9YP3qMI7tgQfstowQ&ip=71.208.112.225&id=o-AFl_MhTlGyV7aKDdCVsLLX4MtjtzTXZAFQp5-jDWKCsm&itag=22&source=youtube&requiressl=yes&mh=LK&mm=31&mn=sn-5uaeznde&ms=au&mv=m&mvi=3&pl=18&initcwndbps=908750&vprv=1&svpuc=1&mime=video%2Fmp4&ns=dYxIDrLEgjg5HrRo3XSeQ1cF&ratebypass=yes&dur=2779.126&lmt=1482936511576053&mt=1618846144&fexp=24001373%2C24007246&c=WEB&n=Fvf51wF5Xdb9rj&sparams=expire%2Cei%2Cip%2Cid%2Citag%2Csource%2Crequiressl%2Cvprv%2Csvpuc%2Cmime%2Cns%2Cratebypass%2Cdur%2Clmt&sig=AOq0QJ8wRQIgcLLQN634M-ZXYDApnzMpf7hbXSnshIC-O7lhZZ78BFQCIQDw3jL9svdaWEU8WICZ6_E1RWmvG2viv73IDS-uiQyJXA%3D%3D&lsparams=mh%2Cmm%2Cmn%2Cms%2Cmv%2Cmvi%2Cpl%2Cinitcwndbps&lsig=AG3C_xAwRgIhAImcGXI7MTFPqyNdXpKcdZfO-Ae8vtiJO8xxr5wuNkf_AiEA34iaOv0x98aqAtCPpnsAfNcMb1VK5gDk3jGocxKrXtM%3D'
[download] You_can_-j_REJECT_but_you_can_not_hide_-_Global_scanning_of_the_IPv6_Internet_33c3_-_deutsche_Ubers-rXUafEqpTvU.mp4 has already been downloaded

[download] 100% of 289.24MiB
[info] Writing video description to: You_can_-j_REJECT_but_you_can_not_hide_-_Global_scanning_of_the_IPv6_Internet_33c3_-_deutsche_Ubers-rXUafEqpTvU.description
[info] Writing video subtitles to: You_can_-j_REJECT_but_you_can_not_hide_-_Global_scanning_of_the_IPv6_Internet_33c3_-_deutsche_Ubers-rXUafEqpTvU.en.vtt
WARNING: Unable to download subtitle for "en": Unable to download webpage: HTTP Error 404: Not Found (caused by <HTTPError 404: 'Not Found'>); please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; see  https://yt-dl.org/update  on how to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.
[debug] Invoking downloader on 'https://r3---sn-5uaeznde.googlevideo.com/videoplayback?expire=1618867984&ei=sKJ9YP3qMI7tgQfstowQ&ip=71.208.112.225&id=o-AFl_MhTlGyV7aKDdCVsLLX4MtjtzTXZAFQp5-jDWKCsm&itag=18&source=youtube&requiressl=yes&mh=LK&mm=31&mn=sn-5uaeznde&ms=au&mv=m&mvi=3&pl=18&initcwndbps=908750&vprv=1&svpuc=1&mime=video%2Fmp4&ns=dYxIDrLEgjg5HrRo3XSeQ1cF&gir=yes&clen=97952227&ratebypass=yes&dur=2779.126&lmt=1482936705634151&mt=1618846144&fexp=24001373%2C24007246&c=WEB&n=Fvf51wF5Xdb9rj&sparams=expire%2Cei%2Cip%2Cid%2Citag%2Csource%2Crequiressl%2Cvprv%2Csvpuc%2Cmime%2Cns%2Cgir%2Cclen%2Cratebypass%2Cdur%2Clmt&sig=AOq0QJ8wRAIgQ-LjNbYDq8p0g02nikvayQO3uO9yuPhYqzi4B17t_H4CIEPDzev4wGA3BSrAocUFXcxsabuXu-b7iPpduybml_aq&lsparams=mh%2Cmm%2Cmn%2Cms%2Cmv%2Cmvi%2Cpl%2Cinitcwndbps&lsig=AG3C_xAwRgIhAImcGXI7MTFPqyNdXpKcdZfO-Ae8vtiJO8xxr5wuNkf_AiEA34iaOv0x98aqAtCPpnsAfNcMb1VK5gDk3jGocxKrXtM%3D'
[download] You_can_-j_REJECT_but_you_can_not_hide_-_Global_scanning_of_the_IPv6_Internet_33c3_-_deutsche_Ubers-rXUafEqpTvU.mp4 has already been downloaded

[download] 100% of 289.24MiB
```

## Description

I waited a few weeks thinking that this would be easily noticed. So far it has not been fixed or reported AFAIK.

I download a youtube video and youtube-dl's request for the subtitle gets a 404 response.
I expect that youtube-dl, when it finds a subtitle, will download it.
This only happens with some videos on youtube.com.
I could probably find more URLs that trigger this if you need them.

Thanks!