Read audio by blocks of 1024 samples

In practice, the system captures audio samples by blocks of 1024
samples.

Remplace the hardcoded value of 5 milliseconds (240 samples), and let
AudioRecord fill the input buffer provided by MediaCodec (or by
AudioRawRecorder), with a maximum size of 1024 samples (just in case).

server/src/main/java/com/genymobile/scrcpy/AudioCapture.java

@@ -24,6 +24,11 @@ public final class AudioCapture {
     public static final int ENCODING = AudioFormat.ENCODING_PCM_16BIT;
     public static final int BYTES_PER_SAMPLE = 2;
 
+    // Never read more than 1024 samples, even if the buffer is bigger (that would increase latency).
+    // A lower value is useless, since the system captures audio samples by blocks of 1024 (so for example if we read by blocks of 256 samples, we
+    // receive 4 successive blocks without waiting, then we wait for the 4 next ones).
+    public static final int MAX_READ_SIZE = 1024 * CHANNELS * BYTES_PER_SAMPLE;
+
     private final int audioSource;
 
     private AudioRecord recorder;
@@ -36,10 +41,6 @@ public final class AudioCapture {
         this.audioSource = audioSource.value();
     }
 
-    public static int millisToBytes(int millis) {
-        return SAMPLE_RATE * CHANNELS * BYTES_PER_SAMPLE * millis / 1000;
-    }
-
     private static AudioFormat createAudioFormat() {
         AudioFormat.Builder builder = new AudioFormat.Builder();
         builder.setEncoding(ENCODING);
@@ -135,8 +136,8 @@ public final class AudioCapture {
     }
 
     @TargetApi(Build.VERSION_CODES.N)
-    public int read(ByteBuffer directBuffer, int size, MediaCodec.BufferInfo outBufferInfo) {
-        int r = recorder.read(directBuffer, size);
+    public int read(ByteBuffer directBuffer, MediaCodec.BufferInfo outBufferInfo) {
+        int r = recorder.read(directBuffer, MAX_READ_SIZE);
         if (r <= 0) {
             return r;
         }

server/src/main/java/com/genymobile/scrcpy/AudioEncoder.java

@@ -37,9 +37,6 @@ public final class AudioEncoder implements AsyncProcessor {
     private static final int SAMPLE_RATE = AudioCapture.SAMPLE_RATE;
     private static final int CHANNELS = AudioCapture.CHANNELS;
 
-    private static final int READ_MS = 5; // milliseconds
-    private static final int READ_SIZE = AudioCapture.millisToBytes(READ_MS);
-
     private final AudioCapture capture;
     private final Streamer streamer;
     private final int bitRate;
@@ -93,7 +90,7 @@ public final class AudioEncoder implements AsyncProcessor {
         while (!Thread.currentThread().isInterrupted()) {
             InputTask task = inputTasks.take();
             ByteBuffer buffer = mediaCodec.getInputBuffer(task.index);
-            int r = capture.read(buffer, READ_SIZE, bufferInfo);
+            int r = capture.read(buffer, bufferInfo);
             if (r <= 0) {
                 throw new IOException("Could not read audio: " + r);
             }

server/src/main/java/com/genymobile/scrcpy/AudioRawRecorder.java

@@ -13,9 +13,6 @@ public final class AudioRawRecorder implements AsyncProcessor {
 
     private Thread thread;
 
-    private static final int READ_MS = 5; // milliseconds
-    private static final int READ_SIZE = AudioCapture.millisToBytes(READ_MS);
-
     public AudioRawRecorder(AudioCapture capture, Streamer streamer) {
         this.capture = capture;
         this.streamer = streamer;
@@ -28,7 +25,7 @@ public final class AudioRawRecorder implements AsyncProcessor {
             return;
         }
 
-        final ByteBuffer buffer = ByteBuffer.allocateDirect(READ_SIZE);
+        final ByteBuffer buffer = ByteBuffer.allocateDirect(AudioCapture.MAX_READ_SIZE);
         final MediaCodec.BufferInfo bufferInfo = new MediaCodec.BufferInfo();
 
         try {
@@ -43,7 +40,7 @@ public final class AudioRawRecorder implements AsyncProcessor {
             streamer.writeAudioHeader();
             while (!Thread.currentThread().isInterrupted()) {
                 buffer.position(0);
-                int r = capture.read(buffer, READ_SIZE, bufferInfo);
+                int r = capture.read(buffer, bufferInfo);
                 if (r < 0) {
                     throw new IOException("Could not read audio: " + r);
                 }