Junlong Zou

For transport without bandwidth estimation, such as `PlainRtpTransport`, we will only change layers when receiving first SR of each stream or there is a change in the score. But in...

Support different rtp header extentions and payload for each consumer.

8

## Feature Request According to WHEP, when subscribing stream, client send `Offer` first, and server replay `Answer` then. So the rtp header extention ids of each consumer may be different....