Android: Ask system for optimal audio buffer size and sample rate

This can reduce audio latency according to
https://developer.android.com/ndk/guides/audio/opensl/opensl-prog-notes#perform.

Previously we were using the hardcoded values of 48000 Hz and 256 frames
per buffer. The sample rate we use with this change is 48000 Hz on all
devices I'm aware of, but the buffer size does vary across devices.

Terminology note: The old code used the term "sample" to refer to what
Android refers to as a "frame". "Frame" is a clearer term to use for
this, so I've changed OpenSLESStream's terminology. One frame consists
of one sample per channel.

2 files changed, 33 insertions, 13 deletions

diff --git a/Source/Core/AudioCommon/OpenSLESStream.cpp b/Source/Core/AudioCommon/OpenSLESStream.cpp
index 84831ceec6..3fc71e75df 100644
--- a/Source/Core/AudioCommon/OpenSLESStream.cpp
+++ b/Source/Core/AudioCommon/OpenSLESStream.cpp
@@ -8,11 +8,13 @@
 
 #include <SLES/OpenSLES.h>
 #include <SLES/OpenSLES_Android.h>
+#include <jni.h>
 
 #include "Common/Assert.h"
 #include "Common/CommonTypes.h"
 #include "Common/Logging/Log.h"
 #include "Core/ConfigManager.h"
+#include "jni/AndroidCommon/IDCache.h"
 
 void OpenSLESStream::BQPlayerCallback(SLAndroidSimpleBufferQueueItf bq, void* context)
 {
@@ -24,8 +26,8 @@ void OpenSLESStream::PushSamples(SLAndroidSimpleBufferQueueItf bq)
   ASSERT(bq == m_bq_player_buffer_queue);
 
   // Render to the fresh buffer
-  m_mixer->Mix(reinterpret_cast<short*>(m_buffer[m_current_buffer]), BUFFER_SIZE_IN_SAMPLES);
-  SLresult result = (*bq)->Enqueue(bq, m_buffer[m_current_buffer], sizeof(m_buffer[0]));
+  m_mixer->Mix(m_buffer[m_current_buffer].data(), m_frames_per_buffer);
+  SLresult result = (*bq)->Enqueue(bq, m_buffer[m_current_buffer].data(), m_bytes_per_buffer);
   m_current_buffer ^= 1;  // Switch buffer
 
   // Comment from sample code:
@@ -36,6 +38,23 @@ void OpenSLESStream::PushSamples(SLAndroidSimpleBufferQueueItf bq)
 
 bool OpenSLESStream::Init()
 {
+  JNIEnv* env = IDCache::GetEnvForThread();
+  jclass audio_utils = IDCache::GetAudioUtilsClass();
+  const SLuint32 sample_rate =
+      env->CallStaticIntMethod(audio_utils, IDCache::GetAudioUtilsGetSampleRate());
+  m_frames_per_buffer =
+      env->CallStaticIntMethod(audio_utils, IDCache::GetAudioUtilsGetFramesPerBuffer());
+
+  INFO_LOG_FMT(AUDIO, "OpenSLES configuration: {} Hz, {} frames per buffer", sample_rate,
+               m_frames_per_buffer);
+
+  constexpr SLuint32 channels = 2;
+  const SLuint32 samples_per_buffer = m_frames_per_buffer * channels;
+  m_bytes_per_buffer = m_frames_per_buffer * channels * sizeof(m_buffer[0][0]);
+
+  for (std::vector<short>& buffer : m_buffer)
+    buffer.resize(samples_per_buffer);
+
   SLresult result;
   // create engine
   result = slCreateEngine(&m_engine_object, 0, nullptr, 0, nullptr, nullptr);
@@ -50,13 +69,11 @@ bool OpenSLESStream::Init()
   ASSERT(SL_RESULT_SUCCESS == result);
 
   SLDataLocator_AndroidSimpleBufferQueue loc_bufq = {SL_DATALOCATOR_ANDROIDSIMPLEBUFFERQUEUE, 2};
-  SLDataFormat_PCM format_pcm = {SL_DATAFORMAT_PCM,
-                                 2,
-                                 m_mixer->GetSampleRate() * 1000,
-                                 SL_PCMSAMPLEFORMAT_FIXED_16,
-                                 SL_PCMSAMPLEFORMAT_FIXED_16,
-                                 SL_SPEAKER_FRONT_LEFT | SL_SPEAKER_FRONT_RIGHT,
-                                 SL_BYTEORDER_LITTLEENDIAN};
+  SLDataFormat_PCM format_pcm = {
+      SL_DATAFORMAT_PCM,           channels,
+      sample_rate * 1000,          SL_PCMSAMPLEFORMAT_FIXED_16,
+      SL_PCMSAMPLEFORMAT_FIXED_16, SL_SPEAKER_FRONT_LEFT | SL_SPEAKER_FRONT_RIGHT,
+      SL_BYTEORDER_LITTLEENDIAN};
 
   SLDataSource audioSrc = {&loc_bufq, &format_pcm};
 
@@ -92,7 +109,7 @@ bool OpenSLESStream::Init()
   m_current_buffer ^= 1;
 
   result = (*m_bq_player_buffer_queue)
-               ->Enqueue(m_bq_player_buffer_queue, m_buffer[0], sizeof(m_buffer[0]));
+               ->Enqueue(m_bq_player_buffer_queue, m_buffer[0].data(), m_bytes_per_buffer);
   if (SL_RESULT_SUCCESS != result)
     return false;
 
diff --git a/Source/Core/AudioCommon/OpenSLESStream.h b/Source/Core/AudioCommon/OpenSLESStream.h
index 009d8d891a..9772f0b9c7 100644
--- a/Source/Core/AudioCommon/OpenSLESStream.h
+++ b/Source/Core/AudioCommon/OpenSLESStream.h
@@ -4,6 +4,9 @@
 #pragma once
 
 #ifdef HAVE_OPENSL_ES
+#include <array>
+#include <vector>
+
 #include <SLES/OpenSLES.h>
 #include <SLES/OpenSLES_Android.h>
 #endif  // HAVE_OPENSL_ES
@@ -35,11 +38,11 @@ private:
   SLAndroidSimpleBufferQueueItf m_bq_player_buffer_queue;
   SLVolumeItf m_bq_player_volume;
 
-  static constexpr int BUFFER_SIZE = 512;
-  static constexpr int BUFFER_SIZE_IN_SAMPLES = BUFFER_SIZE / 2;
+  SLuint32 m_frames_per_buffer;
+  SLuint32 m_bytes_per_buffer;
 
   // Double buffering.
-  short m_buffer[2][BUFFER_SIZE];
+  std::array<std::vector<short>, 2> m_buffer;
   int m_current_buffer = 0;
 #endif  // HAVE_OPENSL_ES
 };