I'm going to need to add a few more compressed formats, WMV which is straightforward, but also AAC (so MPEG v2/v4 audio), and I think wg_format could be cleaned up a bit like this beforehand.
Then, AAC could either be added as a separate
AUDIO_MPEG4 format, or, with an version field, to the (renamed)
AUDIO_MPEG format, though it doesn't share any of the current
AUDIO_MPEG1 properties. FWIW GStreamer caps is
audio/mpeg for both, with an
mpegversion that can be 1, 2 or 4. Could be very well added as
AUDIO_AAC too, I don't really mind.