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Peer connection
...............
* Send `raddr` and `rport` parameters for server reflexive and relayed candidates.
This is required for Firefox to accept our STUN / TURN candidates.
* Do not raise an exception if ICE or DTLS connection fails, just change state.
Media
.....
* Revert to using asyncio's `run_in_executor` to send data to the encoder, it greatly
reduces the response time.
* Adjust package requirements to accept PyAV < 7.0.0.
Examples
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* `webcam` : force Chrome to use "unified-plan" semantics to enabled `addTransceiver`.
* :class:`aiortc.contrib.media.MediaPlayer` : don't sleep at all when playing from webcam.
This eliminates the constant one-second lag in the `webcam` demo.