Calculate audio media drift time from AudioSource

The problem was that the time to receive an output buffer
from an audio encoder is different because the encoder does not
need to read from the source for all output buffers. This leads
to large fluctuation in terms of wall clock duration between two
neighboring audio sample outputs from the audio encoder. As a
result, the media time for the video track after adjustment using
the drifting changes wildly sometimes.

This patch addresses this issue by only updating the media drift
time when an audio source input buffer is read. the wall clock
for the audio track is also calculated at the same time when
the input audio buffer is read at AudioSource.

bug - 2959800

Change-Id: I3174aa182f744784b540f0a7198524d4eee8bd7b

1 files changed, 9 insertions, 20 deletions

diff --git a/media/libstagefright/MPEG4Writer.cpp b/media/libstagefright/MPEG4Writer.cpp
index a15b84e..af2b4c4 100644
--- a/media/libstagefright/MPEG4Writer.cpp
+++ b/media/libstagefright/MPEG4Writer.cpp
@@ -1430,9 +1430,6 @@ status_t MPEG4Writer::Track::threadEntry() {
     int64_t previousPausedDurationUs = 0;
     int64_t timestampUs;
 
-    int64_t wallClockTimeUs = 0;
-    int64_t lastWallClockTimeUs = 0;
-
     sp<MetaData> meta_data;
     bool collectStats = collectStatisticalData();
 
@@ -1542,14 +1539,15 @@ status_t MPEG4Writer::Track::threadEntry() {
             // of neighboring samples. This in turn helps reduce the track header size,
             // especially, the number of entries in the "stts" box.
             if (mNumSamples > 1) {
-                int64_t durationUs = timestampUs + mOwner->getDriftTimeUs() - lastTimestampUs;
+                int64_t currDriftTimeUs = mOwner->getDriftTimeUs();
+                int64_t durationUs = timestampUs + currDriftTimeUs - lastTimestampUs;
                 int64_t diffUs = (durationUs > lastDurationUs)
                             ? durationUs - lastDurationUs
                             : lastDurationUs - durationUs;
                 if (diffUs <= 5000) {  // XXX: Magic number 5ms
                     timestampUs = lastTimestampUs + lastDurationUs;
                 } else {
-                    timestampUs += mOwner->getDriftTimeUs();
+                    timestampUs += currDriftTimeUs;
                 }
             }
         }
@@ -1557,12 +1555,6 @@ status_t MPEG4Writer::Track::threadEntry() {
         if (mNumSamples > 1) {
             if (timestampUs <= lastTimestampUs) {
                 LOGW("Frame arrives too late!");
-#if 0
-                // Drop the late frame.
-                copy->release();
-                copy = NULL;
-                continue;
-#else
                 // Don't drop the late frame, since dropping a frame may cause
                 // problems later during playback
 
@@ -1573,7 +1565,6 @@ status_t MPEG4Writer::Track::threadEntry() {
                 } else {
                     timestampUs = lastTimestampUs + (1000000LL + (mTimeScale >> 1)) / mTimeScale;
                 }
-#endif
             }
         }
 
@@ -1613,12 +1604,10 @@ status_t MPEG4Writer::Track::threadEntry() {
         lastDurationTicks = currDurationTicks;
         lastTimestampUs = timestampUs;
         if (mIsRealTimeRecording && mIsAudio) {
-            wallClockTimeUs = systemTime() / 1000;
-            int64_t wallClockDurationUs = wallClockTimeUs - lastWallClockTimeUs;
-            if (mNumSamples > 2) {
-                mOwner->addDriftTimeUs(lastDurationUs - wallClockDurationUs);
+            int64_t driftTimeUs = 0;
+            if (meta_data->findInt64(kKeyDriftTime, &driftTimeUs)) {
+                mOwner->setDriftTimeUs(driftTimeUs);
             }
-            lastWallClockTimeUs = wallClockTimeUs;
         }
 
         if (isSync != 0) {
@@ -1851,10 +1840,10 @@ void MPEG4Writer::Track::logStatisticalData(bool isAudio) {
     }
 }
 
-void MPEG4Writer::addDriftTimeUs(int64_t driftTimeUs) {
-    LOGV("addDriftTimeUs: %lld us", driftTimeUs);
+void MPEG4Writer::setDriftTimeUs(int64_t driftTimeUs) {
+    LOGV("setDriftTimeUs: %lld us", driftTimeUs);
     Mutex::Autolock autolock(mLock);
-    mDriftTimeUs += driftTimeUs;
+    mDriftTimeUs = driftTimeUs;
 }
 
 int64_t MPEG4Writer::getDriftTimeUs() {