Add GCC-managed encoded Opus audio track#160
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Move Opus audio encoding into the sender so the GCC bandwidth estimator drives audio bitrate alongside video, sharing the bitrate pool. Audio was previously pre-encoded and pushed as a passive track that GCC could not touch. - Generalize EncodedTrack to carry audio (isAudio, audioTrack, audioSource); the existing local track and encodedReader/bitrateTracker are shared by both kinds. - New AddEncodedAudioTrack(trackID, opus.Params): builds the Opus codec selector, AudioBuffer source, mediadevices AudioTrack, and encoded reader, and registers the track in s.tracks so it flows through GCC allocation. - New SendAudioFrame to push raw interleaved PCM. - New sender/audio_buffer.go (AudioBuffer): the audio counterpart to FrameBuffer, with the same initialized-gate non-blocking Read and drop-oldest bounded queue. - updateEncoderBitrate gains a codec.BitRateController branch for Opus, clamped to [8000, 32000] bps. - processEncodedFrames uses a 20ms duration for audio and skips the VP8 keyframe sniff; ForceKeyFrame/recreateEncoder/Close guard on isAudio. - Extract attachTrackToPeerConnection helper (de-dupes AddVideoTrack). The legacy passive AddAudioTrack path is left untouched (additive). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Context
The audio stream is effectively fixed bitrate: audio is pre-encoded outside the sender and pushed as a passive track via
AddAudioTrack, so the GCC bandwidth estimator — which dynamically drives video bitrate — never touches it. When the network degrades, video scales down but audio holds its bandwidth.This makes audio a first-class, GCC-managed encoded Opus track inside the sender, so the same control loop (
updateBitrate→updateEncoderBitrate) that drives VP8 also drives Opus, sharing the GCC bitrate pool. Callers push raw PCM instead of pre-encoded Opus.The change is additive: the legacy passive
AddAudioTrackpath is left untouched.Changes
EncodedTrackto carry audio (isAudio,audioTrack,audioSource); the existing local track andencodedReader/bitrateTracker/mimeTypeare shared by both kinds.AddEncodedAudioTrack(trackID, opus.Params)— builds the Opus codec selector,AudioBuffersource, mediadevicesAudioTrack, and encoded reader; registers the track ins.tracksso it flows through GCC allocation.SendAudioFrame(trackID, pcm, sampleRate, channels)— pushes raw interleaved PCM.sender/audio_buffer.go(AudioBuffer) — the audio counterpart toFrameBuffer: sameinitialized-gate non-blockingReadand drop-oldest bounded queue.updateEncoderBitrategains acodec.BitRateControllerbranch for Opus, clamped to[8000, 32000]bps.processEncodedFramesuses a 20 ms duration for audio and skips the VP8 keyframe sniff;ForceKeyFrame/recreateEncoder/Closeguard onisAudio.attachTrackToPeerConnectionhelper (de-dupesAddVideoTrack).Testing
go build ./...,go vet ./...,golangci-lint run ./...(0 issues), andgo test ./...all pass. New tests insender/audio_buffer_test.gocover buffer behavior, track creation/validation, a full PCM→Opus encode path, and the GCC bitrate-driven path.Note
Downstream consumer wiring (cgo
PushAudioPCMexport, C++ raw-PCM push, Bazel.sore-pin) lives in a separate repo and is out of scope here. For GCC to genuinely drive audio, the encoded audio track must beAddTrack'd on the PeerConnection this sender owns so transport-cc feedback reaches the estimator.🤖 Generated with Claude Code