From 6f82f82abbb9346537f39569b93c41b65d03eca3 Mon Sep 17 00:00:00 2001
From: Cameron Gutman <aicommander@gmail.com>
Date: Fri, 16 Jun 2017 19:08:15 -0700
Subject: [PATCH] Use low latency audio pathway on Lollipop and later

---
 .../binding/audio/AndroidAudioRenderer.java   | 136 ++++++++++++++----
 1 file changed, 105 insertions(+), 31 deletions(-)

diff --git a/app/src/main/java/com/limelight/binding/audio/AndroidAudioRenderer.java b/app/src/main/java/com/limelight/binding/audio/AndroidAudioRenderer.java
index bc297ebe..7fa1d439 100644
--- a/app/src/main/java/com/limelight/binding/audio/AndroidAudioRenderer.java
+++ b/app/src/main/java/com/limelight/binding/audio/AndroidAudioRenderer.java
@@ -1,8 +1,10 @@
 package com.limelight.binding.audio;
 
+import android.media.AudioAttributes;
 import android.media.AudioFormat;
 import android.media.AudioManager;
 import android.media.AudioTrack;
+import android.os.Build;
 
 import com.limelight.LimeLog;
 import com.limelight.nvstream.av.audio.AudioRenderer;
@@ -12,10 +14,50 @@ public class AndroidAudioRenderer implements AudioRenderer {
 
     private AudioTrack track;
 
+    private AudioTrack createAudioTrack(int channelConfig, int bufferSize, boolean lowLatency) {
+        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP) {
+            return new AudioTrack(AudioManager.STREAM_MUSIC,
+                    48000,
+                    channelConfig,
+                    AudioFormat.ENCODING_PCM_16BIT,
+                    bufferSize,
+                    AudioTrack.MODE_STREAM);
+        }
+        else {
+            AudioAttributes.Builder attributesBuilder = new AudioAttributes.Builder()
+                    .setUsage(AudioAttributes.USAGE_GAME);
+
+            if (Build.VERSION.SDK_INT < Build.VERSION_CODES.O) {
+                // Use FLAG_LOW_LATENCY on L through N
+                if (lowLatency) {
+                    attributesBuilder.setFlags(AudioAttributes.FLAG_LOW_LATENCY);
+                }
+            }
+
+            AudioTrack.Builder trackBuilder = new AudioTrack.Builder()
+                    .setAudioFormat(new AudioFormat.Builder()
+                            .setEncoding(AudioFormat.ENCODING_PCM_16BIT)
+                            .setSampleRate(48000)
+                            .setChannelMask(channelConfig)
+                            .build())
+                    .setAudioAttributes(attributesBuilder.build())
+                    .setTransferMode(AudioTrack.MODE_STREAM)
+                    .setBufferSizeInBytes(bufferSize);
+
+            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
+                // Use PERFORMANCE_MODE_LOW_LATENCY on O and later
+                if (lowLatency) {
+                    trackBuilder.setPerformanceMode(AudioTrack.PERFORMANCE_MODE_LOW_LATENCY);
+                }
+            }
+
+            return trackBuilder.build();
+        }
+    }
+
     @Override
     public int setup(int audioConfiguration) {
         int channelConfig;
-        int bufferSize;
         int bytesPerFrame;
 
         switch (audioConfiguration)
@@ -38,44 +80,76 @@ public class AndroidAudioRenderer implements AudioRenderer {
         // do this on many devices and it lowers audio latency.
         // We'll try the small buffer size first and if it fails,
         // use the recommended larger buffer size.
-        try {
-            // Buffer two frames of audio if possible
-            bufferSize = bytesPerFrame * 2;
 
-            track = new AudioTrack(AudioManager.STREAM_MUSIC,
-                    48000,
-                    channelConfig,
-                    AudioFormat.ENCODING_PCM_16BIT,
-                    bufferSize,
-                    AudioTrack.MODE_STREAM);
-            track.play();
-        } catch (Exception e) {
-            // Try to release the AudioTrack if we got far enough
-            try {
-                if (track != null) {
-                    track.release();
-                }
-            } catch (Exception ignored) {}
+        for (int i = 0; i < 4; i++) {
+            boolean lowLatency;
+            int bufferSize;
 
-            // Now try the larger buffer size
-            bufferSize = Math.max(AudioTrack.getMinBufferSize(48000,
+            // We will try:
+            // 1) Small buffer, low latency mode
+            // 2) Large buffer, low latency mode
+            // 3) Small buffer, standard mode
+            // 4) Large buffer, standard mode
+
+            switch (i) {
+                case 0:
+                case 1:
+                    lowLatency = true;
+                    break;
+                case 2:
+                case 3:
+                    lowLatency = false;
+                    break;
+                default:
+                    // Unreachable
+                    throw new IllegalStateException();
+            }
+
+            switch (i) {
+                case 0:
+                case 2:
+                    bufferSize = bytesPerFrame * 2;
+                    break;
+
+                case 1:
+                case 3:
+                    // Try the larger buffer size
+                    bufferSize = Math.max(AudioTrack.getMinBufferSize(48000,
                             channelConfig,
                             AudioFormat.ENCODING_PCM_16BIT),
-                    bytesPerFrame * 2);
+                            bytesPerFrame * 2);
 
-            // Round to next frame
-            bufferSize = (((bufferSize + (bytesPerFrame - 1)) / bytesPerFrame) * bytesPerFrame);
+                    // Round to next frame
+                    bufferSize = (((bufferSize + (bytesPerFrame - 1)) / bytesPerFrame) * bytesPerFrame);
+                    break;
+                default:
+                    // Unreachable
+                    throw new IllegalStateException();
+            }
 
-            track = new AudioTrack(AudioManager.STREAM_MUSIC,
-                    48000,
-                    channelConfig,
-                    AudioFormat.ENCODING_PCM_16BIT,
-                    bufferSize,
-                    AudioTrack.MODE_STREAM);
-            track.play();
+            // Skip low latency options if hardware sample rate isn't 48000Hz
+            if (AudioTrack.getNativeOutputSampleRate(AudioManager.STREAM_MUSIC) != 48000 && lowLatency) {
+                continue;
+            }
+
+            try {
+                track = createAudioTrack(channelConfig, bufferSize, lowLatency);
+                track.play();
+
+                // Successfully created working AudioTrack. We're done here.
+                LimeLog.info("Audio track configuration: "+bufferSize+" "+lowLatency);
+                break;
+            } catch (Exception e) {
+                // Try to release the AudioTrack if we got far enough
+                try {
+                    if (track != null) {
+                        track.release();
+                        track = null;
+                    }
+                } catch (Exception ignored) {}
+            }
         }
 
-        LimeLog.info("Audio track buffer size: "+bufferSize);
         return 0;
     }