Extract channel mixing matrix construction out of AudioMixer - #3200
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jemoreira
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Sep 18, 2026
AudioMixer::OnPlayback built its channel map by writing the stream volume onto the diagonal of a shared 6x6 identity member, under the mixer lock. Move that into a standalone audio_channel_matrix unit and build the matrix locally. No functional change: ConvertAudioStream only reads [i][j] for i < dst_channels and j < src_channels, so the dst x src diagonal is identical to the old 6x6 one. Keeping the mixing math in a standalone unit makes it testable on its own and gives a single place to add spatial processing (fade, balance, ducking, ITU-R BS.775 downmixing) later on. This is a part of set of PRs to support car audio controls (fade/balance/ducking/mute/focus). Bug: b/563302839
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AudioMixer::OnPlayback built its channel map by writing the stream volume onto
the diagonal of a shared 6x6 identity member, under the mixer lock. Move that
into a standalone audio_channel_matrix unit and build the matrix locally.
No functional change: ConvertAudioStream only reads [i][j] for i < dst_channels
and j < src_channels, so the dst x src diagonal is identical to the old 6x6 one.
This is a part of set of PRs to support car audio controls (fade/balance/ducking/mute/focus).
Bug: b/563302839