Convert record channel mask for dynamic mix

When creating the AudioRecord instance for a dynamic mix, convert
  the output channel mask of the mix to an input channel mask
  to be used by the AudioRecord instance through which the
  mixed audio is rerouted.

Bug 16009464

Change-Id: I3addbe85339f6f06b69acc3f9b8e2a765e5d7305

media/java/android/media/AudioFormat.java

@@ -126,6 +126,29 @@ public class AudioFormat {
             CHANNEL_OUT_LOW_FREQUENCY);
     // CHANNEL_OUT_ALL is not yet defined; if added then it should match AUDIO_CHANNEL_OUT_ALL
 
+    /**
+     * @hide
+     * Return the input channel mask corresponding to an output channel mask.
+     * This can be used for submix rerouting for the mask of the recorder to map to that of the mix.
+     * @param outMask a combination of the CHANNEL_OUT_* definitions, but not CHANNEL_OUT_DEFAULT
+     * @return a combination of CHANNEL_IN_* definitions matching an output channel mask
+     * @throws IllegalArgumentException
+     */
+    public static int inChannelMaskFromOutChannelMask(int outMask) throws IllegalArgumentException {
+        if (outMask == CHANNEL_OUT_DEFAULT) {
+            throw new IllegalArgumentException(
+                    "Illegal CHANNEL_OUT_DEFAULT channel mask for input.");
+        }
+        switch (channelCountFromOutChannelMask(outMask)) {
+            case 1:
+                return CHANNEL_IN_MONO;
+            case 2:
+                return CHANNEL_IN_STEREO;
+            default:
+                throw new IllegalArgumentException("Unsupported channel configuration for input.");
+        }
+    }
+
     /**
      * @hide
      * Return the number of channels from an input channel mask

media/java/android/media/audiopolicy/AudioPolicy.java

@@ -155,6 +155,7 @@ public class AudioPolicy {
         {
             throw new IllegalArgumentException("Invalid AudioMix: not defined for loop back");
         }
+        // TODO also check mix is defined for playback or recording, and matches forTrack argument
     }
 
     /**
@@ -175,13 +176,19 @@ public class AudioPolicy {
             return null;
         }
         checkMixReadyToUse(mix, false/*not for an AudioTrack*/);
+        // create an AudioFormat from the mix format compatible with recording, as the mix
+        // was defined for playback
+        AudioFormat mixFormat = new AudioFormat.Builder(mix.getFormat())
+                .setChannelMask(AudioFormat.inChannelMaskFromOutChannelMask(
+                        mix.getFormat().getChannelMask()))
+                .build();
         // create the AudioRecord, configured for loop back, using the same format as the mix
         AudioRecord ar = new AudioRecord(
                 new AudioAttributes.Builder()
                         .setInternalCapturePreset(MediaRecorder.AudioSource.REMOTE_SUBMIX)
                         .addTag(mix.getRegistration())
                         .build(),
-                mix.getFormat(),
+                mixFormat,
                 AudioRecord.getMinBufferSize(mix.getFormat().getSampleRate(),
                         // using stereo for buffer size to avoid the current poor support for masks
                         AudioFormat.CHANNEL_IN_STEREO, mix.getFormat().getEncoding()),