Matroska audio-only files are not useable as instrumental tracks

[odrling]

I found out recently that one of our instrumental tracks wasn’t working properly as it was using a Matroska audio-only file.
It happens because filetype.guess relies on magic numbers to detect the filetype, which can’t easily tell the difference between an audio-only matroska file (.mka) and video matroska file (.mkv). Instead it recognizes the matroska file format and returns video/x-matroska. I would assume that it also happens with .m4a and .ogg files which also use a container format that can hold video tracks.

The easy way out would be to use mimetypes.guess_file_type which does differentiate the two by relying on the file extension. But I suppose that it was meant as a quick check that the file is indeed an audio file.

To check the file content while supporting these container formats I would suggest relying on mediainfo or ffmpeg to check that the file contains only an audio track.

[Neraste]

We initially didn’t want to rely on the extension of a file because there is no guarantee that it corresponds to its content. But we never thought that using the magic number would give unexpected results on video containers (now, it’s obvious when I say it loud). Seems like we didn’t check different audio files extensively enough (even if a few are checked, and ogg is considered as an audio file type). I think the problem could be solved by first checking the extension, then double checking the magic number (and allowing video or audio type).

A thing that I just realized, the feeder already detects an extra audio file, or an extra audio track, but this data is only saved as a has_instrumental Boolean on the server, and the player re-detects the file or the track again. I’m not sure why we ended up with this design. The extra audio file should be saved on the server too, and the player should not try to detect it. I think I will implement it for version 1.11 (not the immediate next one).

I can do a quick fix on both projects for now, I guess.

If I’m not wrong, you use a different feeder than Dakara feeder, so you’ll have to reflect this change on your side.

[odrling]

If I’m not wrong, you use a different feeder than Dakara feeder, so you’ll have to reflect this change on your side.

That sounds like it would be easy to implement in karaberus too, and we also check the files for correctness before feeding to dakara. In fact my hotfix for the player for our setup was just to trust that the name.mka file is correct if it exists odrling@83a9677