Fix aux channels not decaying

[mathesoncalum]

Resolves: musescore/MuseScore#34534

The problem here is that aux.processed can only ever flip to true in writeTrackToAuxBuffers which, since 7e9e6ed, doesn't get called if all of its senders are silent. The result is that aux channels are cut off abruptly once the senders go silent because processAuxChannels won't write anything to the buffer when aux.processed is false.

The solution proposed here is to continue writing to the buffer in processAuxChannels if the aux itself is not silent (due to reverb ringing out, etc.)

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ℹ️ Recent review info

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Reviewing files that changed from the base of the PR and between b17807d and 330939b.

📒 Files selected for processing (1)

• framework/audio/engine/internal/mixer.cpp

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📝 Walkthrough

Walkthrough

The mixer adds isChainSilent to centralize chain silence checks. process skips silent main tracks before writing to output or auxiliary buffers. processAuxChannels continues processing auxiliary chains that may still produce audio, such as reverberation tails, and skips silent auxiliary chains during output mixing.

Priority: ⬇️ Low

Severity of issue fixed: Low

Merge Risk: ⚪ Minimal · up to 33093

The auxiliary processing change preserves non-silent effect tails while continuing to suppress silent chains; no actionable merge risk remains.

🚥 Pre-merge checks | ✅ 3 | ❌ 2

❌ Failed checks (2 warnings)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description states the linked issue, explains the regression, and describes the proposed fix. However, it omits the required checklist and build configuration from the repository template, includi…	Complete the required template sections. Mark each applicable checklist item, provide the contributor username for the CLA, describe manual or automated testing, and retain or explicitly address the build configuration section.
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 4 functions across 1 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the primary change: preventing aux channels from stopping their decay when their senders become silent.
Linked Issues check	✅ Passed	The change addresses #34534. processAuxChannels now processes an aux channel when it received input or its chain is not silent. This allows reverb output to decay and keeps writing non-silent aux ou…
Out of Scope Changes check	✅ Passed	The diff changes only framework/audio/engine/internal/mixer.cpp. The helper, processing changes, and comments directly support the aux-channel decay fix in #34534. No unrelated behavior or files are…

Full details: Description check

Explanation

The description states the linked issue, explains the regression, and describes the proposed fix. However, it omits the required checklist and build configuration from the repository template, including CLA status, testing, coding guidelines, unnecessary-change review, and test coverage.

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[mathesoncalum]

/build

[github-actions]

Build dispatched: https://github.com/musescore/muse_framework/actions/runs/34823344478