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fix(audio): fix SDL backend buffer sizing issues causing audio cuts/glitches when CPU is struggling #1107

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fix(audio): fix SDL backend buffer sizing issues causing audio cuts/glitches when CPU is struggling #1107

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2 changes: 1 addition & 1 deletion include/ship/audio/SDLAudioPlayer.h
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Original file line number Diff line number Diff line change
Expand Up @@ -50,6 +50,6 @@ class SDLAudioPlayer final : public AudioPlayer {

private:
SDL_AudioDeviceID mDevice = 0; ///< Handle to the opened SDL audio device.
int32_t mNumChannels = 2; ///< Number of output channels (2 for stereo, 6 for 5.1).
uint8_t mNumChannels = 2; ///< Number of output channels (2 for stereo, 6 for 5.1).
};
} // namespace Ship
37 changes: 22 additions & 15 deletions src/ship/audio/SDLAudioPlayer.cpp
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Expand Up @@ -13,37 +13,47 @@ void SDLAudioPlayer::DoClose() {
if (mDevice != 0) {
// Pause playback first
SDL_PauseAudioDevice(mDevice, 1);
// Clear any queued audio to prevent glitches when reopening

// Prevent stale audio when reopening
SDL_ClearQueuedAudio(mDevice);
SDL_CloseAudioDevice(mDevice);
mDevice = 0;
}
}

bool SDLAudioPlayer::DoInit() {
if (SDL_Init(SDL_INIT_AUDIO) != 0) {
if (SDL_InitSubSystem(SDL_INIT_AUDIO) != 0) {
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SPDLOG_ERROR("SDL init error: {}", SDL_GetError());
return false;
}

// Always open with the correct number of output channels
mNumChannels = this->GetNumOutputChannels();

SDL_AudioSpec want, have;
SDL_zero(want);

want.freq = this->GetSampleRate();
want.format = AUDIO_S16SYS;
want.channels = mNumChannels;
want.samples = this->GetSampleLength();
want.callback = NULL;
want.channels = this->GetNumOutputChannels();

// Increase backend/device buffering slightly
// to reduce rare underruns/glitches.
//
// IMPORTANT:
// This is NOT part of the emulator buffering logic.
// It only affects SDL/backend latency.
want.samples = GetSampleLength() * 2;
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want.callback = nullptr;

mDevice = SDL_OpenAudioDevice(nullptr, 0, &want, &have, 0);

mDevice = SDL_OpenAudioDevice(NULL, 0, &want, &have, 0);
if (mDevice == 0) {
SPDLOG_ERROR("SDL_OpenAudio error: {}", SDL_GetError());
SPDLOG_ERROR("SDL_OpenAudioDevice error: {}", SDL_GetError());
return false;
}

SPDLOG_INFO("SDL Audio initialized: {} channels, {} Hz", mNumChannels, this->GetSampleRate());
mNumChannels = have.channels;

SPDLOG_INFO("SDL audio initialized: {} Hz, {} channels, {} samples", have.freq, have.channels, have.samples);

SDL_PauseAudioDevice(mDevice, 0);
return true;
Expand All @@ -54,9 +64,6 @@ int SDLAudioPlayer::Buffered() {
}

void SDLAudioPlayer::DoPlay(const uint8_t* buf, size_t len) {
if (Buffered() < 6000) {
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// Don't fill the audio buffer too much in case this happens
SDL_QueueAudio(mDevice, buf, len);
}
SDL_QueueAudio(mDevice, buf, len);
}
} // namespace Ship
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