Crashes when SDL backend requires pow2 quantum (OSS, Emscripten)

[jbeich]

Regressed by a0f859c

$ cmake -DBUILD_TESTS=ON
$ make

$ SDL_AUDIODRIVER=dsp ./faudio_tests
INFO: OpenAudioDevice failed: Fragment size must be a power of two
WARN:

Assertion failure at FAudio_PlatformInit (src/FAudio_platform_sdl2.c:133), triggered 1 time:
  '0 && "Failed to open audio device!"'

Abort/Break/Retry/Ignore/AlwaysIgnore? [abriA] : A

Process 26959 stopped
* thread #1, name = 'faudio_tests', stop reason = signal SIGSEGV: invalid address (fault address: 0xd4)
    frame #0: 0x000000080028fd9a libFAudio.so.0`FAudio_INTERNAL_VoiceOutputFrequency(voice=0x000000080f62d000, pSendList=0x0000000000000000) at FAudio_internal.c:1415:48
   1412         if ((pSendList == NULL) || (pSendList->SendCount == 0))
   1413         {
   1414                 /* When we're deliberately given no sends, use master rate! */
-> 1415                 outSampleRate = voice->audio->master->master.inputSampleRate;
   1416         }
   1417         else
   1418         {
(lldb) bt
* thread #1, name = 'faudio_tests', stop reason = signal SIGSEGV: invalid address (fault address: 0xd4)
  * frame #0: 0x000000080028fd9a libFAudio.so.0`FAudio_INTERNAL_VoiceOutputFrequency(voice=0x000000080f62d000, pSendList=0x0000000000000000) at FAudio_internal.c:1415:48
    frame #1: 0x0000000800281dbe libFAudio.so.0`FAudio_CreateSourceVoice(audio=0x000000080f62c000, ppSourceVoice=0x00007fffffffdfc8, pSourceFormat=0x00007fffffffdfa0, Flags=0, MaxFrequencyRatio=1, pCallback=0x000000000020a170, pSendList=0x0000000000000000, pEffectChain=0x0000000000000000) at FAudio.c:477:2
    frame #2: 0x0000000000203d8a faudio_tests`test_simple_streaming(xa=0x000000080f62c000) at xaudio2.c:370:5
    frame #3: 0x0000000000203435 faudio_tests`main(argc=1, argv=0x00007fffffffe098) at xaudio2.c:1279:13
    frame #4: 0x000000000020315f faudio_tests`_start(ap=<unavailable>, cleanup=<unavailable>) at crt1.c:76:7

[flibitijibibo]

This sounds like an issue with SDL - when the backend has specific needs for sample period size it should override the value and trigger creation of an SDL_AudioStream to act as a buffer between the client and server. You’ll see this with both the WASAPI and PulseAudio backends.

[flibitijibibo]

Confirmed, this is the issue: https://hg.libsdl.org/SDL/file/22dcbdfe45ea/src/audio/dsp/SDL_dspaudio.c#l211

This should be falling back to a nearest-power-of-two, which will trigger an SDL_AudioStream in SDL. I would report this at the SDL Bugzilla (maybe CC whoever maintains SDL for FreeBSD), this already works with other backends.

[flibitijibibo]

Emscripten is affected by this as well:

https://hg.libsdl.org/SDL/file/4709c1dfeabb/src/audio/emscripten/SDL_emscriptenaudio.c#l192

[flibitijibibo]

SDL issue has been filed: https://bugzilla.libsdl.org/show_bug.cgi?id=5136

[flibitijibibo]

SDL issue was moved to GitHub: libsdl-org/SDL#3685

[flibitijibibo]

Doing a bit of spring cleaning...

See libsdl-org/SDL#3685 for more on this issue, on the FAudio side this is closed as NOTOURBUG.