Extract audio recorder interface

In order to support both encoded and raw audio stream, extract a
interface (very minimal, but sufficient to just start and stop).

PR #3757 <Genymobile/scrcpy#3757>

Author: rom1v

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

@@ -14,7 +14,7 @@
 import java.util.concurrent.ArrayBlockingQueue;
 import java.util.concurrent.BlockingQueue;
 
-public final class AudioEncoder {
+public final class AudioEncoder implements AudioRecorder {
 
     private static class InputTask {
         private final int index;

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

@@ -0,0 +1,12 @@
+package com.genymobile.scrcpy;
+
+/**
+ * A component able to record audio asynchronously
+ *
+ * The implementation is responsible to send packets.
+ */
+public interface AudioRecorder {
+    void start();
+    void stop();
+    void join() throws InterruptedException;
+}

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

@@ -92,7 +92,7 @@ private static void scrcpy(Options options) throws IOException, ConfigurationExc
         }
 
         Controller controller = null;
-        AudioEncoder audioEncoder = null;
+        AudioRecorder audioRecorder = null;
 
         try (DesktopConnection connection = DesktopConnection.open(scid, tunnelForward, audio, control, sendDummyByte)) {
             if (options.getSendDeviceMeta()) {
@@ -111,8 +111,8 @@ private static void scrcpy(Options options) throws IOException, ConfigurationExc
             if (audio) {
                 Streamer audioStreamer = new Streamer(connection.getAudioFd(), options.getAudioCodec(), options.getSendCodecId(),
                         options.getSendFrameMeta());
-                audioEncoder = new AudioEncoder(audioStreamer, options.getAudioBitRate(), options.getAudioCodecOptions(), options.getAudioEncoder());
-                audioEncoder.start();
+                audioRecorder = new AudioEncoder(audioStreamer, options.getAudioBitRate(), options.getAudioCodecOptions(), options.getAudioEncoder());
+                audioRecorder.start();
             }
 
             Streamer videoStreamer = new Streamer(connection.getVideoFd(), options.getVideoCodec(), options.getSendCodecId(),
@@ -131,17 +131,17 @@ private static void scrcpy(Options options) throws IOException, ConfigurationExc
         } finally {
             Ln.d("Screen streaming stopped");
             initThread.interrupt();
-            if (audioEncoder != null) {
-                audioEncoder.stop();
+            if (audioRecorder != null) {
+                audioRecorder.stop();
             }
             if (controller != null) {
                 controller.stop();
             }
 
             try {
                 initThread.join();
-                if (audioEncoder != null) {
-                    audioEncoder.join();
+                if (audioRecorder != null) {
+                    audioRecorder.join();
                 }
                 if (controller != null) {
                     controller.join();