Branch: refs/heads/main
Home: https://github.com/WebKit/WebKit
Commit: 27d3de8f8b2289fbcba9812b6eb37d16a3db96fd
https://github.com/WebKit/WebKit/commit/27d3de8f8b2289fbcba9812b6eb37d16a3db96fd
Author: Ahmad Saleem <[email protected]>
Date: 2026-07-26 (Sun, 26 Jul 2026)
Changed paths:
A
LayoutTests/imported/w3c/web-platform-tests/webaudio/the-audio-api/the-oscillatornode-interface/sub-sample-start-expected.txt
A
LayoutTests/imported/w3c/web-platform-tests/webaudio/the-audio-api/the-oscillatornode-interface/sub-sample-start.html
M Source/WebCore/Modules/webaudio/OscillatorNode.cpp
Log Message:
-----------
OscillatorNode with a-rate automation ignores sub-sample start time and
begins out of phase
https://bugs.webkit.org/show_bug.cgi?id=320277
rdar://183194827
Reviewed by Chris Dumez.
This patch aligns WebKit with Gecko / Firefox.
When an oscillator is started at a sub-sample-accurate time,
OscillatorNode::process() advances the initial virtualReadIndex by the
fractional start offset scaled by one phase increment, so the oscillator
begins at the correct sub-sample phase. That compensation was written as
`startFrameOffset * frequency * rateScale`, but `frequency` is a local
that is only assigned in the k-rate (!hasSampleAccurateValues) branch.
Whenever a-rate frequency or detune automation is active, `frequency`
stays 0, so the compensation term is 0 and the oscillator starts on the
frame boundary instead of at the requested sub-sample offset, i.e.
audibly out of phase.
Use the first sample-accurate phase increment (phaseIncrements[0]) for
the compensation when hasSampleAccurateValues is true, falling back to
frequency * rateScale for the k-rate case. For a constant frequency the
two are identical, so this only changes behavior when automation is
active.
This matches the k-rate path, which already advances by
`frequency * rateScale` per frame.
Test:
imported/w3c/web-platform-tests/webaudio/the-audio-api/the-oscillatornode-interface/sub-sample-start.html
*
LayoutTests/imported/w3c/web-platform-tests/webaudio/the-audio-api/the-oscillatornode-interface/sub-sample-start-expected.txt:
Added.
*
LayoutTests/imported/w3c/web-platform-tests/webaudio/the-audio-api/the-oscillatornode-interface/sub-sample-start.html:
Added.
* Source/WebCore/Modules/webaudio/OscillatorNode.cpp:
(WebCore::OscillatorNode::process):
Canonical link: https://commits.webkit.org/317953@main
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