The spec is clearly under-specified because we have the case of numberOfInputs = numberOfOutputs = 1 so the second item is applicable.  But outputChannelCount is specified, but that item doesn't say what to do in this case.

I'll file an issue with the spec to get this clarified.

Not sure hos this works in other browsers because right now no other browser implements AudioWorklets. :-)

Thanks for looking into this!

For those following along, the issue has been logged as:

https://github.com/WebAudio/web-audio-api/issues/1686

> Not sure hos this works in other browsers because right now no other browser implements AudioWorklets. :-)

Hah, sorry about that. That would be a failing of my use of the bug reporting wizard.

Talked to hongchan@ about this (who wrote most of the AudioWorklet spec) and he thinks the intent is always to use the computed channels when inputs = outputs = 1.

Do you know what the rationale for this choice might be? While defaulting to the computed channel count when no other outputChannelCount is provided is clearly a very useful feature, it seems like not allowing this to be overridden is an artificial limitation.

As a concrete example of an application this restriction might present consider custom up-mixing/down-mixing logic implemented within an AudioWorklet.

There are obviously potential workarounds such as adding a dummy output/input or using channel splitters/mergers but this doesn't seem ideal.

Thanks rtoy@ and hongchan@ for your help!

We'll have to discuss this, but it seems reasonable to let outputChannelCount override the computed count.  I don't really remember the full rationale, but we definitely wanted an AudioWorklet to be able to emulate the behavior of a Gain node.

I guess we have the mutual agreement now:
https://github.com/WebAudio/web-audio-api/issues/1686#issuecomment-404285949

I will fix this when we merge the spec PR.

PR is under the review:
https://github.com/WebAudio/web-audio-api/pull/1710

PR is merged and we're ready to do this.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b9a938fe9706bdeb853e768b30917be01dba47dd

commit b9a938fe9706bdeb853e768b30917be01dba47dd
Author: Hongchan Choi <hongchan@chromium.org>
Date: Tue Sep 11 19:09:21 2018

Honor given outputChannelCount for AudioWorkletNodeOptions

When both input and output are 1 in AudioWorkletNode, it ignores
the output channel count specified by user. Fix this incorrect behavior
so the specified channel count can be honored properly.

See also: https://webaudio.github.io/web-audio-api/#configuring-channels-with-audioworkletnodeoptions

Bug:  861681 
Test: webaudio/the-audio-api/the-audioworklet-interface/audioworkletnode-output-channel-count.https.html
Change-Id: Ie5cc7f3a5a2b48c67cdf39e93bde8477bfedae89
Reviewed-on: https://chromium-review.googlesource.com/1216072
Commit-Queue: Hongchan Choi <hongchan@chromium.org>
Reviewed-by: Raymond Toy <rtoy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#590432}
[add] https://crrev.com/b9a938fe9706bdeb853e768b30917be01dba47dd/third_party/WebKit/LayoutTests/external/wpt/webaudio/the-audio-api/the-audioworklet-interface/audioworkletnode-output-channel-count.https.html
[add] https://crrev.com/b9a938fe9706bdeb853e768b30917be01dba47dd/third_party/WebKit/LayoutTests/external/wpt/webaudio/the-audio-api/the-audioworklet-interface/processors/channel-count-processor.js
[modify] https://crrev.com/b9a938fe9706bdeb853e768b30917be01dba47dd/third_party/blink/renderer/modules/webaudio/audio_worklet_node.cc
[modify] https://crrev.com/b9a938fe9706bdeb853e768b30917be01dba47dd/third_party/blink/renderer/modules/webaudio/audio_worklet_node.h