Request 20 ms audio frames on Steam Link to reduce CPU overhead

app/streaming/audio/audio.cpp

@@ -41,6 +41,7 @@ bool Session::testAudio(int audioConfiguration)
     // the renderer the channel count and sample rate.
     OPUS_MULTISTREAM_CONFIGURATION opusConfig = {};
     opusConfig.sampleRate = 48000;
+    opusConfig.samplesPerFrame = 240;
 
     switch (audioConfiguration)
     {
@@ -143,7 +144,7 @@ void Session::arDecodeAndPlaySample(char* sampleData, int sampleLength)
     s_ActiveSession->m_AudioSampleCount++;
 
     if (s_ActiveSession->m_AudioRenderer != nullptr) {
-        int desiredSize = sizeof(short) * SAMPLES_PER_FRAME * s_ActiveSession->m_AudioConfig.channelCount;
+        int desiredSize = sizeof(short) * s_ActiveSession->m_AudioConfig.samplesPerFrame * s_ActiveSession->m_AudioConfig.channelCount;
         void* buffer = s_ActiveSession->m_AudioRenderer->getAudioBuffer(&desiredSize);
         if (buffer == nullptr) {
             return;

app/streaming/audio/renderers/sdlaud.cpp

@@ -31,7 +31,7 @@ bool SdlAudioRenderer::prepareForPlayback(const OPUS_MULTISTREAM_CONFIGURATION*
     // frames contain a non-power of 2 number of samples,
     // so the slop would require buffering another full frame.
     // Specifying non-Po2 seems to work for our supported platforms.
-    want.samples = SAMPLES_PER_FRAME;
+    want.samples = opusConfig->samplesPerFrame;
 
     m_AudioDevice = SDL_OpenAudioDevice(NULL, 0, &want, &have, 0);
     if (m_AudioDevice == 0) {
@@ -41,7 +41,7 @@ bool SdlAudioRenderer::prepareForPlayback(const OPUS_MULTISTREAM_CONFIGURATION*
         return false;
     }
 
-    m_AudioBuffer = malloc(SAMPLES_PER_FRAME * sizeof(short) * opusConfig->channelCount);
+    m_AudioBuffer = malloc(opusConfig->samplesPerFrame * sizeof(short) * opusConfig->channelCount);
     if (m_AudioBuffer == nullptr) {
         SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
                      "Failed to allocate audio buffer");

app/streaming/audio/renderers/slaud.cpp

@@ -2,16 +2,9 @@
 
 #include <SDL.h>
 
-// To reduce CPU load on the Steam Link, we need to accumulate several frames
-// before submitting for playback. Higher frames per submission saves more CPU
-// but increases audio latency.
-#define FRAMES_PER_SUBMISSION 4
-
 SLAudioRenderer::SLAudioRenderer()
     : m_AudioContext(nullptr),
-      m_AudioStream(nullptr),
-      m_AudioBuffer(nullptr),
-      m_AudioBufferBytesFilled(0)
+      m_AudioStream(nullptr)
 {
     SLAudio_SetLogFunction(SLAudioRenderer::slLogCallback, nullptr);
 }
@@ -25,7 +18,7 @@ bool SLAudioRenderer::prepareForPlayback(const OPUS_MULTISTREAM_CONFIGURATION* o
         return false;
     }
 
-    m_AudioBufferSize = SAMPLES_PER_FRAME * sizeof(short) * opusConfig->channelCount * FRAMES_PER_SUBMISSION;
+    m_AudioBufferSize = opusConfig->samplesPerFrame * sizeof(short) * opusConfig->channelCount;
     m_AudioStream = SLAudio_CreateStream(m_AudioContext,
                                          opusConfig->sampleRate,
                                          opusConfig->channelCount,
@@ -45,29 +38,12 @@ bool SLAudioRenderer::prepareForPlayback(const OPUS_MULTISTREAM_CONFIGURATION* o
 
 void* SLAudioRenderer::getAudioBuffer(int* size)
 {
-    SDL_assert(*size == m_AudioBufferSize / FRAMES_PER_SUBMISSION);
-
-    if (m_AudioBuffer == nullptr) {
-        m_AudioBufferBytesFilled = 0;
-        m_AudioBuffer = (char*)SLAudio_BeginFrame(m_AudioStream);
-        if (m_AudioBuffer == nullptr) {
-            return nullptr;
-        }
-    }
-
-    return (void*)&m_AudioBuffer[m_AudioBufferBytesFilled];
+    SDL_assert(*size == m_AudioBufferSize);
+    return SLAudio_BeginFrame(m_AudioStream);
 }
 
 SLAudioRenderer::~SLAudioRenderer()
 {
-    if (m_AudioBuffer != nullptr) {
-        // We had a buffer in flight when we quit. Just in case
-        // SLAudio doesn't handle this properly, we'll zero and submit
-        // it just to be safe.
-        memset(m_AudioBuffer, 0, m_AudioBufferSize);
-        SLAudio_SubmitFrame(m_AudioStream);
-    }
-
     if (m_AudioStream != nullptr) {
         SLAudio_FreeStream(m_AudioStream);
     }
@@ -77,18 +53,9 @@ SLAudioRenderer::~SLAudioRenderer()
     }
 }
 
-bool SLAudioRenderer::submitAudio(int bytesWritten)
+bool SLAudioRenderer::submitAudio(int)
 {
-    m_AudioBufferBytesFilled += bytesWritten;
-
-    // Submit the buffer when it's full
-    SDL_assert(m_AudioBufferBytesFilled <= m_AudioBufferSize);
-    if (m_AudioBufferBytesFilled == m_AudioBufferSize) {
-        SLAudio_SubmitFrame(m_AudioStream);
-        m_AudioBuffer = nullptr;
-        m_AudioBufferBytesFilled = 0;
-    }
-
+    SLAudio_SubmitFrame(m_AudioStream);
     return true;
 }
 

app/streaming/audio/renderers/slaud.h

@@ -22,7 +22,5 @@ private:
     CSLAudioContext* m_AudioContext;
     CSLAudioStream* m_AudioStream;
 
-    char* m_AudioBuffer;
     int m_AudioBufferSize;
-    int m_AudioBufferBytesFilled;
 };

app/streaming/audio/renderers/soundioaudiorenderer.cpp

@@ -260,7 +260,7 @@ bool SoundIoAudioRenderer::prepareForPlayback(const OPUS_MULTISTREAM_CONFIGURATI
     m_RingBuffer = soundio_ring_buffer_create(m_SoundIo,
                                               m_OutputStream->bytes_per_sample *
                                               m_OpusChannelCount *
-                                              SAMPLES_PER_FRAME *
+                                              opusConfig->samplesPerFrame *
                                               packetsToBuffer);
     if (m_RingBuffer == nullptr) {
         SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,

moonlight-common-c/moonlight-common-c

@@ -1 +1 @@
-Subproject commit 1154cb1d3db53215e46b3c7d2476b27d52d0dfbf
+Subproject commit 59481c085a7f774c5d30374636f8bc75da7c676c