A AudioTrack is a default audio Track, with a AUDIO track_type and "audio/x-raw(ANY)" caps.
By default, an audio track will have its restriction_caps set to "audio/x-raw" with the following properties:
These fields are needed for negotiation purposes, but you can change their values if you wish. It is advised that you do so using update_restriction_caps with new values for the fields you wish to change, and any additional fields you may want to add. Unlike using set_restriction_caps, this will ensure that these default fields will at least have some value set.