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AAudio never uses the MMAP path for a stream with a session ID, while a low latency stream still gets a FAST track on the legacy path. This gives a way to stay off MMAP without the conservative profile, which on some devices sends the stream to a deep buffer output with a high latency. The option is carried into the config rebuilt on a reroute, like the other AAudio settings.
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🟡 Changes recommended
A critical active finding remains because miniaudio.h assigns AAudioStreamBuilder_setSessionId unconditionally under MA_NO_RUNTIME_LINKING, which can fail to compile on Android targets below API 28 due to the symbol not being declared without an API-level guard.
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What changed in this PR
Adds an AAudio-specific configuration flag to request allocation of an Android audio session ID, enabling low-latency playback while staying on the legacy (non-MMAP) path for improved robustness on affected devices.
Changes:
- Added
ma_device_config.aaudio.allocateSessionIdand persisted it throughma_devicestate and the AAudio reroute reinit path. - Added runtime/dynamic loading support for
AAudioStreamBuilder_setSessionId()and applied it during stream builder configuration when requested. - Documented the new option alongside other AAudio device configuration settings.
| File | Description |
|---|---|
| miniaudio.h | Updated as part of this pull request. |
Review effort: Balanced
| pContext->aaudio.AAudioStreamBuilder_setUsage = (ma_proc)AAudioStreamBuilder_setUsage; | ||
| pContext->aaudio.AAudioStreamBuilder_setContentType = (ma_proc)AAudioStreamBuilder_setContentType; | ||
| pContext->aaudio.AAudioStreamBuilder_setInputPreset = (ma_proc)AAudioStreamBuilder_setInputPreset; | ||
| pContext->aaudio.AAudioStreamBuilder_setSessionId = (ma_proc)AAudioStreamBuilder_setSessionId; |
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Summary
Adds
aaudio.allocateSessionIdtoma_device_config. When set, the stream is opened withAAUDIO_SESSION_ID_ALLOCATE. AAudio never uses the MMAP path for a stream with a session ID(
AudioStreamBuilder::build(): "MMAP not used because sessionId specified"), while a low latencystream still gets a FAST track on the legacy path (
AudioStreamTrack::open()).Why
We need a low latency stream that stays off MMAP. On a Samsung Galaxy Z Fold5 (Android 17) an MMAP
stream fails to start after a system sound with haptics (see #1184): the HAL cannot route it and
AAudio returns
AAUDIO_ERROR_DISCONNECTEDafter about a second. The conservative profile avoidsMMAP too, but Samsung's audio policy sends that stream to its deep buffer output, about 0.2 s of
latency, audible on every button press.
With a session ID the stream gets
AUDIO_OUTPUT_FLAG_FASTon the low latency output, and launchesin that state play normally. AudioFlinger grants a FAST track only when the stream runs at the
output's sample rate, so we open the device with
sampleRate = 0.Details
allocateSessionIdis stored inma_device.aaudioand carried into the config rebuilt inma_device_reinit__aaudio(), like the other AAudio settings (see AAudio: allowSetBufferCapacity is not preserved across a reroute, so the configured buffer size is silently lost #1158), so a reroute does notbring MMAP back.
AAudioStreamBuilder_setSessionId()is API 28. It is loaded with the other functions and skippedwhen missing. With
MA_NO_RUNTIME_LINKINGit is linked directly, next toAAudioStreamBuilder_setUsage(), which is API 28 as well.aaudio.noAutoStartAfterReroute.Testing
MMAP not used because sessionId specified,AUDIO_OUTPUT_FLAG_FAST successfulandgot Legacy ... perf = LL. Three launchesright after a system sound with haptics all played; without the option 5 out of 5 such launches
failed.
-std=c89 -Wall -Wextra -Wpedantic), with andwithout
MA_NO_RUNTIME_LINKING, with no new warnings.dev-0.12hasaaudio.performanceModebut no session ID either. Happy to port this there if youwant it.