Store the size to context because different streams may have different
maximum payload sizes. For example, an SRTP stream with RTP authentication
enabled has a smaller payload size than a normal RTP stream.
Instead of using uvgRTP's internal RTP timestamps, let user specify
timestamp for the media when push_frame() is called.
Instead of propagating the timestamp through the send stack, store
the timestamp value temporarily to the RTP context of the media
stream and reset it after push_frame() is done.
User should not mix and match uvgRTP's internal RTP timestamps with
custom timestamps so either all of the calls or none of the calls should
given a timestamp to push_frame().
Custom timestamps should be increased in accordance with the media clock
rate, otherwise problems may occur with media reception.
Aaro Altonen