Support WebM

[duracellh]

Running Fedora 30 with the distro repo versions of quodlibet and mutagen. I believe this is probably a mutagen issue but let me know if you think it isn't.

I am unable to queue, "Add a file", etc any .opus file. When I try, nothing happens at all in the gui, but the console shows this (1 line per file attempted):

E: 59.505: formats._misc.MusicFile: xiph.py:505:loader: quodlibet.formats._misc.AudioFileError: file type could not be determined
E: 74.348: formats._misc.MusicFile: xiph.py:505:loader: quodlibet.formats._misc.AudioFileError: file type could not be determined

Package versions:
quodlibet 4.2.1-3.fc30
exfalso 4.2.1-3.fc30
python3-feedparser 5.2.1-9.fc30
python3-musicbrainzngs 0.5-14.fc30
python3-mutagen 1.42.0-2.fc30

gstreamer versions:

gstreamer1-1.16.0-1.fc30.i686
gstreamer1-plugins-good-qt-1.16.0-1.fc30.x86_64
gstreamer1-plugins-good-gtk-1.16.0-1.fc30.x86_64
gstreamer1-plugins-base-1.16.0-1.fc30.i686
gstreamer1-plugins-ugly-1.16.0-2.fc30.x86_64
gstreamer1-plugins-good-1.16.0-1.fc30.x86_64
gstreamer1-plugins-good-extras-1.16.0-1.fc30.x86_64
gstreamer1-plugins-ugly-free-1.16.0-2.fc30.x86_64
gstreamer1-plugins-bad-free-1.16.0-2.fc30.x86_64
PackageKit-gstreamer-plugin-1.1.12-5.fc30.x86_64
gstreamer1-libav-1.16.0-1.fc30.x86_64
phonon-backend-gstreamer-4.9.0-11.fc30.x86_64
gstreamer1-plugins-base-1.16.0-1.fc30.x86_64
gstreamer1-plugins-bad-free-extras-1.16.0-2.fc30.x86_64
libnice-gstreamer1-0.1.16-5.fc30.x86_64
gstreamer1-1.16.0-1.fc30.x86_64
phonon-qt5-backend-gstreamer-4.9.0-11.fc30.x86_64
gstreamer1-plugins-bad-freeworld-1.16.0-1.fc30.x86_64

[lazka]

Thanks. Can you send me a file per email? reiter.christoph@gmail.com

[duracellh]

After more testing, this is not exactly what I thought. If I encode an opus file myself, it works perfectly as expected.
The files that were failing all came from youtube via youtube-dl/ffmpeg. What is strange is that if I fake re-encode them (ffmpeg -i input.opus -c:a copy output.opus), the same audio stream and everything, the resulting file works without issue so it must be something with the way youtube or youtube-dl are doing things. Other audio files from youtube-dl .m4a work normally.
Granted these opus files work fine in other audio players, so perhaps there is something to be done there, so I will send a coupe exmaples.

[lazka]

Those are .webm files containing opus. And we don't support webm yet. I guess ffmpeg converts them to ogg opus files.

[hvitis]

bumping