Fix audio PTS when not monotonically increasing

Some decoders fail to guarantee that PTS must be monotonically
increasing. Fix the PTS when they're not.

Fixes #4054 <https://github.com/Genymobile/scrcpy/issues/4054>

doc/audio.md

@@ -30,8 +30,9 @@ To disable only the audio playback, see [no playback](video.md#no-playback).
 
 To play audio only, disable the video:
 
-```
+```bash
 scrcpy --no-video
+# interrupt with Ctrl+C
 ```
 
 Without video, the audio latency is typically not criticial, so it might be

doc/video.md

@@ -168,6 +168,7 @@ the computer. This option is useful when [recording](recording.md) or when
 ```bash
 scrcpy --v4l2-sink=/dev/video2 --no-playback
 scrcpy --record=file.mkv --no-playback
+# interrupt with Ctrl+C
 ```
 
 It is also possible to disable video and audio playback separately:

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

@@ -163,7 +163,7 @@ public final class AudioCapture {
             //  - an estimation from the previous PTS and the packet size as a fallback.
             //
             // Therefore, the property that PTS are monotonically increasing is no guaranteed in corner cases, so enforce it.
-            pts = previousPts + 1;
+            pts = previousPts;
         }
         previousPts = pts;
 

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

@@ -105,8 +105,17 @@ public final class AudioEncoder implements AsyncProcessor {
     private void outputThread(MediaCodec mediaCodec) throws IOException, InterruptedException {
         streamer.writeAudioHeader();
 
+        long lastPts = 0;
         while (!Thread.currentThread().isInterrupted()) {
             OutputTask task = outputTasks.take();
+
+            if (task.bufferInfo.presentationTimeUs < lastPts) {
+                // Fix PTS if not monotonically increasing
+                task.bufferInfo.presentationTimeUs = lastPts;
+            } else {
+                lastPts = task.bufferInfo.presentationTimeUs;
+            }
+
             ByteBuffer buffer = mediaCodec.getOutputBuffer(task.index);
             try {
                 streamer.writePacket(buffer, task.bufferInfo);