987976 - MediaStreamAudioSourceNode/MediaElementAudioSourceNode output channel count should not depend on channelCountMode

Status: RESOLVED FIXED

Description

[Karl Tomlinson (:karlt)]

"The number of channels of the output corresponds to the number of channels of the AudioMediaStreamTrack.  If there is no valid audio track, then the number of channels output will be one silent channel."

AudioNodeExternalInputStream should not be using AudioNodeStream::ComputeFinalOuputChannelCount() because that is intended for input up/down mixing.  MediaStreamAudioSourceNode has no inputs.

channelCountMode defaults to max and so will have no effect unless set.

See also https://github.com/WebAudio/web-audio-api/issues/286#issuecomment-33511528

Comment 1

[Karl Tomlinson (:karlt)]

Attachment: make AudioNodeExternalInputStream output channel count match stream, unless > MaxChannelCount

The difference from Blink here is that Blink plays silence for if element
channel counts are > 32, but here more channels are down-mixed.  Media stream
channel counts are also fixed to 2 in Blink, but that restriction is not
applied here.

Leaving the "inline" const static/class member initialization of
MaxChannelCount left missing symbols with gcc 4.7.3.

Comment 2

[Karl Tomlinson (:karlt)]

Attachment: rename ComputeFinalOuputChannelCount ComputedNumberOfChannels to match spec

to remove any implication that the function might be for calculating
the number of output channels for an AudioNode.

Comment 3

[Karl Tomlinson (:karlt)]

https://hg.mozilla.org/integration/mozilla-inbound/rev/4af100e74537
https://hg.mozilla.org/integration/mozilla-inbound/rev/348747dd115f

Comment 4

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/4af100e74537
https://hg.mozilla.org/mozilla-central/rev/348747dd115f