WIP: Seek on all streams
The problem: This check is wrong: priv->blocking_msg_received == nbr_active_streams (media). Because when there are 2 stream but only 1 is complete, we will get a timing problem if the incomplete stream prerolls first.
The solution: Remove that check, so that now we always wait for all streams to preroll.
The consequential problem: If we have a pipeline with 2 separate streams, one is complete, the other one is not. When we do a seek on it, only the complete stream will receive the seek event. Therefore only this stream will preroll.
This patch: Send the seek event to all streams. If the stream is complete, send the seek event to the sink like usual. If not, send to the corresponding src_pad in the rtpbin. Now all streams will preroll.