The ContentType attribute describes “what” you are playing.
It expresses the general category of the content. This information is optional.
But in case it is known (for instance Movie for a
movie streaming service or Speech for
an audio book application) this information might be used by the audio framework to
enforce audio focus.
The Usage attribute expresses “why” you are playing a sound, what is this sound used for.
This information is used by certain platforms or routing policies
to make more refined volume or routing decisions.