make Mixxx mime type aware

[Daniel Schürmann]

To improve the detection of various media files. It will be nice to rely on the mime-type detection, rather use the file extension.
We may use libmagic or the Qt 5 mime type support.

[Uwe Klotz (uklotzde-deactivatedaccount)]

This is actually a serious bug that may cause various issues:

https://mixxx.discourse.group/t/mixxx-has-stopped-plaing-newly-downloaded-mp3s/23074/21

I have also seen weird decoded audio signals produced by SoundSourceMP3 which might damage output devices. The combination of the dreaded MP3 format in combination with the ancient libmad library for decoding is dangerous.

[Uwe Klotz (uklotzde-deactivatedaccount)]

https://github.com/mixxxdj/mixxx/pull/4356
https://github.com/mixxxdj/mixxx/pull/4357

[Uwe Klotz (uklotzde-deactivatedaccount)]

This bug is not fixed completely in 2.3.2. Mixxx still detects the wrong MIME type and tries to open the file with the registered SoundSources.

On Linux some tracks with the wrong file extension can be played if FFmpeg is enabled, because it is capable of playing almost every format and kicks in as a fallback SoundSource. On Windows and macOS .mp3 files that actually contain an AAC stream in DASH container as reported by the user will probably fail to play such a file file.

Even 2.4.x does not fix the wrong file type in Mixxx of previously imported files. I will take a look.

[Uwe Klotz (uklotzde-deactivatedaccount)]

Follow-up: https://github.com/mixxxdj/mixxx/pull/4608

[Swiftb0y (swiftb0y)]

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/7970