Provides a base class for RTP depayloaders
out_buf to the peer of filter. This function takes ownership of Unlike
push_ts, this function will not apply any timestamp on the outgoing
buffer. Subclasses should therefore timestamp outgoing buffers themselves.
out_list to the peer of filter. This function takes ownership of
out_buf to the peer of filter. This function takes ownership of Unlike
push, this function will by default apply the last incomming timestamp on
the outgoing buffer when it didn't have a timestamp already. The set_get_timestamp vmethod can be overwritten to change this behaviour
(and take, for example, timestamp into account).
