Bug 960873: Part 7: Reduce apple mp3 MAX_AUDIO_FRAMES to minimize alloc slop. r=cpearce

content/media/apple/AppleMP3Reader.cpp

@@ -12,8 +12,12 @@
 #define AUDIO_READ_BYTES 4096
 
 // Maximum number of audio frames we will accept from the audio decoder in one
-// go.
-#define MAX_AUDIO_FRAMES 4096
+// go.  Carefully select this to work well with both the mp3 1152 max frames
+// per block and power-of-2 allocation sizes.  Since we must pre-allocate the
+// buffer we cannot use AudioCompactor without paying for an additional
+// allocation and copy.  Therefore, choosing a value that divides exactly into
+// 1152 is most memory efficient.
+#define MAX_AUDIO_FRAMES 128
 
 namespace mozilla {
 
@@ -201,7 +205,8 @@ AppleMP3Reader::AudioSampleCallback(UInt32 aNumBytes,
   LOGD("got %u bytes, %u packets\n", aNumBytes, aNumPackets);
 
   // 1 frame per packet * num channels * 32-bit float
-  uint32_t decodedSize = MAX_AUDIO_FRAMES * mAudioChannels * 4;
+  uint32_t decodedSize = MAX_AUDIO_FRAMES * mAudioChannels *
+                         sizeof(AudioDataValue);
 
   // descriptions for _decompressed_ audio packets. ignored.
   nsAutoArrayPtr<AudioStreamPacketDescription>
@@ -238,6 +243,14 @@ AppleMP3Reader::AudioSampleCallback(UInt32 aNumBytes,
       break;
     }
 
+    // If we decoded zero frames then AudiOConverterFillComplexBuffer is out
+    // of data to provide.  We drained its internal buffer completely on the
+    // last pass.
+    if (numFrames == 0 && rv == kNeedMoreData) {
+      LOGD("FillComplexBuffer out of data exactly\n");
+      break;
+    }
+
     int64_t time = FramesToUsecs(mCurrentAudioFrame, mAudioSampleRate).value();
     int64_t duration = FramesToUsecs(numFrames, mAudioSampleRate).value();