Downloading playlist with "mp4" option doesn't download audio

[MMauro94]

Describe the bug The downloaded files have no audio tracks.

To Reproduce Download a playlist with the options "Video and audio", "mp4" and "best".

Expected behavior The audio track is downloaded.

Tested running the docker image on Docker Desktop for Windows, using Linux containers.

Additional context The run command, from the app log: /usr/local/bin/youtube-dl --ignore-errors -f bestvideo[ext=mp4] -o downloads/playlists/%(playlist)s/%(title)s.%(ext)s https://www.youtube.com/playlist?list=XXXXXXX (Playlist ID redacted)

Also, a suggestion: since most people will want to customize their youtube-dl command, why not provide an option to specify a custom command?

[XiovV]

I'll implement the custom youtube-dl feature once I fix #79, #80 and #81