This callback would be useful in the following use case:
The parent spawns children that are supposed to receive a stream
The parent negotiates with the other party to start sending the stream
The spawned children may or may not be ready to receive the stream at that point. To be sure, the parent could negotiate the start of the stream in handle_spec_playing
Possibly we would also need handle_spec_setup for the same reason.
This callback would be useful in the following use case:
handle_spec_playing
Possibly we would also need
handle_spec_setup
for the same reason.