Vsaiortc

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Data channels
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* Emit a warning if the crcmod C extension is not present.

Media
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* Support subsequent offer / answer exchanges.
* Route RTCP parameters to RTP receiver and sender independently.
* Fix a regression when the remote SSRC are not known.
* Fix VP8 descriptor parsing errors detected by fuzzing.
* Fix H264 descriptor parsing errors detected by fuzzing.

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Media
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* Add support for RTX retransmission packets.
* Fix RTP and RTCP parsing errors detected by fuzzing.
* Use case-insensitive comparison for hash algorithm in SDP, fixes interoperability with Asterisk.
* Offer NACK PLI and REMB feedback mechanisms for H.264.

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Data channels
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* Raise an exception if :meth:`RTCDataChannel.send` is called when readyState is not `'open'`.
* Do not use stream sequence number for unordered data channels.

Media
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* Set VP8 target bitrate according to Receiver Estimated Maximum Bandwidth.

Examples
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* Correctly handle encoding in copy-and-paste signaling.
* `server` : add command line options to use HTTPS.
* `webcam` : add command line options to use HTTPS.
* `webcam` : add code to open webcam on OS X.

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* Rework code in order to facilitate garbage collection and avoid memory leaks.

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Media
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* Make AudioStreamTrack and VideoStreamTrack produce empty frames more regularly.

Examples
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* Fix a regession in copy-and-paste signaling which blocked the event loop.

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Peer connection
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* 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
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* 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:`~vsaiortc.contrib.media.MediaPlayer` : don't sleep at all when playing from webcam.
This eliminates the constant one-second lag in the `webcam` demo.