Capture device audio

Create an AudioRecorder to capture the audio source REMOTE_SUBMIX.

For now, the captured packets are just logged into the console.

PR #3757 <https://github.com/Genymobile/scrcpy/pull/3757>

Co-authored-by: Romain Vimont <rom@rom1v.com>
Signed-off-by: Romain Vimont <rom@rom1v.com>

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

@@ -0,0 +1,80 @@
+package com.genymobile.scrcpy;
+
+import android.annotation.SuppressLint;
+import android.annotation.TargetApi;
+import android.media.AudioFormat;
+import android.media.AudioRecord;
+import android.media.MediaRecorder;
+import android.os.Build;
+
+public final class AudioEncoder {
+
+    private static final int SAMPLE_RATE = 48000;
+    private static final int CHANNEL_CONFIG = AudioFormat.CHANNEL_IN_STEREO;
+    private static final int CHANNELS = 2;
+    private static final int FORMAT = AudioFormat.ENCODING_PCM_16BIT;
+    private static final int BYTES_PER_SAMPLE = 2;
+
+    private static final int READ_MS = 5; // milliseconds
+    private static final int READ_SIZE = SAMPLE_RATE * CHANNELS * BYTES_PER_SAMPLE * READ_MS / 1000;
+
+    private Thread thread;
+
+    private static AudioFormat createAudioFormat() {
+        AudioFormat.Builder builder = new AudioFormat.Builder();
+        builder.setEncoding(FORMAT);
+        builder.setSampleRate(SAMPLE_RATE);
+        builder.setChannelMask(CHANNEL_CONFIG);
+        return builder.build();
+    }
+
+    @TargetApi(Build.VERSION_CODES.M)
+    @SuppressLint({"WrongConstant", "MissingPermission"})
+    private static AudioRecord createAudioRecord() {
+        AudioRecord.Builder builder = new AudioRecord.Builder();
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.S) {
+            // On older APIs, Workarounds.fillAppInfo() must be called beforehand
+            builder.setContext(FakeContext.get());
+        }
+        builder.setAudioSource(MediaRecorder.AudioSource.REMOTE_SUBMIX);
+        builder.setAudioFormat(createAudioFormat());
+        int minBufferSize = AudioRecord.getMinBufferSize(SAMPLE_RATE, CHANNEL_CONFIG, FORMAT);
+        // This buffer size does not impact latency
+        builder.setBufferSizeInBytes(8 * minBufferSize);
+        return builder.build();
+    }
+
+    public void start() {
+        AudioRecord recorder = createAudioRecord();
+
+        thread = new Thread(() -> {
+            recorder.startRecording();
+            try {
+                byte[] buf = new byte[READ_SIZE];
+                while (!Thread.currentThread().isInterrupted()) {
+                    int r = recorder.read(buf, 0, READ_SIZE);
+                    if (r > 0) {
+                        Ln.i("Audio captured: " + r + " bytes");
+                    } else {
+                        Ln.e("Audio capture error: " + r);
+                    }
+                }
+            } finally {
+                recorder.stop();
+            }
+        });
+        thread.start();
+    }
+
+    public void stop() {
+        if (thread != null) {
+            thread.interrupt();
+        }
+    }
+
+    public void join() throws InterruptedException {
+        if (thread != null) {
+            thread.join();
+        }
+    }
+}

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

@@ -72,7 +72,7 @@ public final class Server {
         boolean sendDummyByte = options.getSendDummyByte();
 
         Workarounds.prepareMainLooper();
-        if (Build.BRAND.equalsIgnoreCase("meizu")) {
+
         // Workarounds must be applied for Meizu phones:
         //  - <https://github.com/Genymobile/scrcpy/issues/240>
         //  - <https://github.com/Genymobile/scrcpy/issues/365>
@@ -81,10 +81,19 @@ public final class Server {
         // But only apply when strictly necessary, since workarounds can cause other issues:
         //  - <https://github.com/Genymobile/scrcpy/issues/940>
         //  - <https://github.com/Genymobile/scrcpy/issues/994>
+        boolean mustFillAppInfo = Build.BRAND.equalsIgnoreCase("meizu");
+
+        // Before Android 11, audio is not supported.
+        // Since Android 12, we can properly set a context on the AudioRecord.
+        // Only on Android 11 we must fill app info for the AudioRecord to work.
+        mustFillAppInfo |= audio && Build.VERSION.SDK_INT == Build.VERSION_CODES.R;
+
+        if (mustFillAppInfo) {
             Workarounds.fillAppInfo();
         }
 
         Controller controller = null;
+        AudioEncoder audioEncoder = null;
 
         try (DesktopConnection connection = DesktopConnection.open(scid, tunnelForward, audio, control, sendDummyByte)) {
             VideoCodec codec = options.getCodec();
@@ -101,6 +110,11 @@ public final class Server {
                 device.setClipboardListener(text -> controllerRef.getSender().pushClipboardText(text));
             }
 
+            if (audio) {
+                audioEncoder = new AudioEncoder();
+                audioEncoder.start();
+            }
+
             Streamer videoStreamer = new Streamer(connection.getVideoFd(), codec, options.getSendCodecId(), options.getSendFrameMeta());
             ScreenEncoder screenEncoder = new ScreenEncoder(device, videoStreamer, options.getBitRate(), options.getMaxFps(),
                     codecOptions, options.getEncoderName(), options.getDownsizeOnError());
@@ -116,12 +130,18 @@ public final class Server {
         } finally {
             Ln.d("Screen streaming stopped");
             initThread.interrupt();
+            if (audioEncoder != null) {
+                audioEncoder.stop();
+            }
             if (controller != null) {
                 controller.stop();
             }
 
             try {
                 initThread.join();
+                if (audioEncoder != null) {
+                    audioEncoder.join();
+                }
                 if (controller != null) {
                     controller.join();
                 }