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As part of go/coil update code search links to not point to the "master" branch. Bug: chromium:1226942 Change-Id: I0ae9e84ecc660f789a69fe0b226f93bbc39a8a66 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/226081 Commit-Queue: Tony Herre <toprice@chromium.org> Reviewed-by: Harald Alvestrand <hta@webrtc.org> Cr-Commit-Position: refs/heads/master@{#34531}
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The WebRTC Audio Mixer Module
The WebRTC audio mixer module is responsible for mixing multiple incoming audio
streams (sources) into a single audio stream (mix). It works with 10 ms frames,
it supports sample rates up to 48 kHz and up to 8 audio channels. The API is
defined in
api/audio/audio_mixer.h
and it includes the definition of
AudioMixer::Source,
which describes an incoming audio stream, and the definition of
AudioMixer,
which operates on a collection of
AudioMixer::Source
objects to produce a mix.
AudioMixer::Source
A source has different characteristic (e.g., sample rate, number of channels,
muted state) and it is identified by an SSRC1.
AudioMixer::Source::GetAudioFrameWithInfo()
is used to retrieve the next 10 ms chunk of audio to be mixed.
AudioMixer
The interface allows to add and remove sources and the
AudioMixer::Mix()
method allows to generates a mix with the desired number of channels.
WebRTC implementation
The interface is implemented in different parts of WebRTC:
AudioMixer
is thread-safe. The output sample rate of the generated mix is automatically
assigned depending on the sample rate of the sources; whereas the number of
output channels is defined by the caller2. Samples from the non-muted sources
are summed up and then a limiter is used to apply soft-clipping when needed.
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A synchronization source (SSRC) is the source of a stream of RTP packets, identified by a 32-bit numeric SSRC identifier carried in the RTP header so as not to be dependent upon the network address (see RFC 3550). ↩︎
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audio/utility/channel_mixer.his used to mix channels in the non-trivial cases - i.e., if the number of channels for a source or the mix is greater than 3. ↩︎