The format descriptions of the media samples referenced by the track.
Mac Catalyst 13.0+
The array contains CMFormatDescriptions (see CMFormatDescriptionRef), each of which indicates the format of media samples referenced by the track.
Asset tracks commonly present uniform media (for example, encoded according to the same encoding settings) and will contain a single format description. However, there are cases where an asset track may contain multiple format descriptions. For instance, an H.264-encoded video track may have some of its segments encoded using the Main profile and others using the High profile. Additionally, an individual AVCompositionTrack, which is a subclass of AVAssetTrack, may contain audio or video segments using different codecs (aac, mp3, aiff, etc.).
You can use the CMFormatDescriptionRef to access low-level details about the media referenced by the track. For instance, you could retrieve the details of track’s media type and subtype as follows: