Intent to Implement and Ship: WebAudio ChannelSplitterNode channelCount and mode are constants

[Raymond Toy]

Title:

Contact emails

rt...@chromium.org, hong...@chromium.org

Spec

http://webaudio.github.io/web-audio-api/

https://webaudio.github.io/web-audio-api/#the-channelsplitternode-interface

Summary

Simplify the behavior of the ChannelSplitterNode by making the channelCount and channelCountMode attributes constant.

Motivation

In the previous version, the channelCount and channelCountMode of the ChannelSplitterNode could be changed. Depending on the values, this would cause the input to be up or downmixed to some number of channels and then up or downmixed for the output before being split into the individual channels for output. By changing the default values and making them constant, the interpretation and usage of the node is simplified. Setting channelCount to the number of outputs and channelCountMode to "explicit" means the input is untouched and then split into the appropriate number of outputs.

This also makes it consistent with the ChannelMergerNode which has constant values as well.

Interoperability and Compatibility Risk

The new default values are compatible with the previous (but different) values for channelCount and channelCountMode. A http archive search (by @hongchan) indicates that no pages actually change the channelCount or channelCountMode of a ChannelSplitterNode. https://www.chromestatus.com/metrics/feature/timeline/popularity/635 indicates barely any usage of this node.

Ongoing technical constraints

None

Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, Chrome OS, Android, and Android WebView)?

Yes.

OWP launch tracking bug

http://crbug.com/653234

Link to entry on the feature dashboard

https://www.chromestatus.com/feature/4701085050601472

Requesting approval to ship?

Yes

[Chris Harrelson]

LGTM1

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[Philip Jägenstedt]

LGTM2, thanks for the compat analysis.

I changed http://crbug.com/653234 into an OWP launch bug, and the spec change is also linked from there, which was helpful to understand the change. (Nothing is made readonly in WebIDL, but attempts to modify will throw.)

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[Jochen Eisinger]

lgtm3