MediaPlayerService: Remove unnecessary zero writes to AudioSink

Causes glitches in PCM playback for NuPlayer callback mode.

Not sure the original intention of this with AwesomePlayer, as zeroes
are only placed under EOS condition for AudioSink targets, not AudioTrack
targets.  Does not seem useful anymore as AwesomePlayer appears to
call stop() which should send the remaining track data out.

Bug: 21198655
Change-Id: Iab80dd7bc6e2e341f92406c5d8f8085e9d877bcd

1 files changed, 17 insertions, 10 deletions

diff --git a/media/libmediaplayerservice/MediaPlayerService.cpp b/media/libmediaplayerservice/MediaPlayerService.cpp
index 7c40121..ee6a85a 100644
--- a/media/libmediaplayerservice/MediaPlayerService.cpp
+++ b/media/libmediaplayerservice/MediaPlayerService.cpp
@@ -1851,20 +1851,23 @@ void MediaPlayerService::AudioOutput::CallbackWrapper(
                 me, buffer->raw, buffer->size, me->mCallbackCookie,
                 CB_EVENT_FILL_BUFFER);
 
-        if ((me->mFlags & AUDIO_OUTPUT_FLAG_COMPRESS_OFFLOAD) == 0 &&
-            actualSize == 0 && buffer->size > 0 && me->mNextOutput == NULL) {
-            // We've reached EOS but the audio track is not stopped yet,
-            // keep playing silence.
+        // Log when no data is returned from the callback.
+        // (1) We may have no data (especially with network streaming sources).
+        // (2) We may have reached the EOS and the audio track is not stopped yet.
+        // Note that AwesomePlayer/AudioPlayer will only return zero size when it reaches the EOS.
+        // NuPlayerRenderer will return zero when it doesn't have data (it doesn't block to fill).
+        //
+        // This is a benign busy-wait, with the next data request generated 10 ms or more later;
+        // nevertheless for power reasons, we don't want to see too many of these.
 
-            memset(buffer->raw, 0, buffer->size);
-            actualSize = buffer->size;
-        }
+        ALOGV_IF(actualSize == 0 && buffer->size > 0, "callbackwrapper: empty buffer returned");
 
+        me->mBytesWritten += actualSize;  // benign race with reader.
         buffer->size = actualSize;
         } break;
 
-
     case AudioTrack::EVENT_STREAM_END:
+        // currently only occurs for offloaded callbacks
         ALOGV("callbackwrapper: deliver EVENT_STREAM_END");
         (*me->mCallback)(me, NULL /* buffer */, 0 /* size */,
                 me->mCallbackCookie, CB_EVENT_STREAM_END);
@@ -1877,11 +1880,15 @@ void MediaPlayerService::AudioOutput::CallbackWrapper(
         break;
 
     case AudioTrack::EVENT_UNDERRUN:
-        // This occurs when there is no data available, typically occurring
+        // This occurs when there is no data available, typically
         // when there is a failure to supply data to the AudioTrack.  It can also
         // occur in non-offloaded mode when the audio device comes out of standby.
         //
-        // If you see this at the start of playback, there probably was a glitch.
+        // If an AudioTrack underruns it outputs silence. Since this happens suddenly
+        // it may sound like an audible pop or glitch.
+        //
+        // The underrun event is sent once per track underrun; the condition is reset
+        // when more data is sent to the AudioTrack.
         ALOGI("callbackwrapper: EVENT_UNDERRUN (discarded)");
         break;