commit 4ecbea3ae1fcefb082dc419cb663909536138ddb
author Wei Jia <wjia@google.com> Tue Oct 20 18:09:57 2015 -0700
committer Wei Jia <wjia@google.com> Wed Oct 21 18:47:35 2015 +0000
tree 07256849cc0586e8f6d3b77cac86b2b562dabe42
parent 422bf879ed138202f7731d5f279c64af5af7da42

MediaClock: prevent media time from going backwards.

Media Clock is started only when AudioSink has rendered some frames.

Bug: 25074321
Change-Id: Ic09fc666eed019e24f5b6a4b8929021eab87ca41

media/libmediaplayerservice/nuplayer/NuPlayerRenderer.cpp

diff --git a/media/libmediaplayerservice/nuplayer/NuPlayerRenderer.cpp b/media/libmediaplayerservice/nuplayer/NuPlayerRenderer.cpp
index 879b825..c7456e9 100644
--- a/media/libmediaplayerservice/nuplayer/NuPlayerRenderer.cpp
+++ b/media/libmediaplayerservice/nuplayer/NuPlayerRenderer.cpp
@@ -313,8 +313,33 @@
     msg->post();
 }
 
-// Called on any threads.
+// Called on any threads without mLock acquired.
 status_t NuPlayer::Renderer::getCurrentPosition(int64_t *mediaUs) {
+    status_t result = mMediaClock->getMediaTime(ALooper::GetNowUs(), mediaUs);
+    if (result == OK) {
+        return result;
+    }
+
+    // MediaClock has not started yet. Try to start it if possible.
+    {
+        Mutex::Autolock autoLock(mLock);
+        if (mAudioFirstAnchorTimeMediaUs == -1) {
+            return result;
+        }
+
+        AudioTimestamp ts;
+        status_t res = mAudioSink->getTimestamp(ts);
+        if (res != OK) {
+            return result;
+        }
+
+        // AudioSink has rendered some frames.
+        int64_t nowUs = ALooper::GetNowUs();
+        int64_t nowMediaUs = getPlayedOutAudioDurationUs(nowUs)
+                + mAudioFirstAnchorTimeMediaUs;
+        mMediaClock->updateAnchor(nowMediaUs, nowUs, -1);
+    }
+
     return mMediaClock->getMediaTime(ALooper::GetNowUs(), mediaUs);
 }
 
@@ -1010,9 +1035,14 @@
         return;
     }
     setAudioFirstAnchorTimeIfNeeded_l(mediaTimeUs);
-    int64_t nowUs = ALooper::GetNowUs();
-    int64_t nowMediaUs = mediaTimeUs - getPendingAudioPlayoutDurationUs(nowUs);
-    mMediaClock->updateAnchor(nowMediaUs, nowUs, mediaTimeUs);
+
+    AudioTimestamp ts;
+    status_t res = mAudioSink->getTimestamp(ts);
+    if (res == OK) {
+        int64_t nowUs = ALooper::GetNowUs();
+        int64_t nowMediaUs = mediaTimeUs - getPendingAudioPlayoutDurationUs(nowUs);
+        mMediaClock->updateAnchor(nowMediaUs, nowUs, mediaTimeUs);
+    }
     mAnchorNumFramesWritten = mNumFramesWritten;
     mAnchorTimeMediaUs = mediaTimeUs;
 }

media/libstagefright/MediaClock.cpp

diff --git a/media/libstagefright/MediaClock.cpp b/media/libstagefright/MediaClock.cpp
index 2641e4e..3aa0061 100644
--- a/media/libstagefright/MediaClock.cpp
+++ b/media/libstagefright/MediaClock.cpp
@@ -25,6 +25,10 @@
 
 namespace android {
 
+// Maximum allowed time backwards from anchor change.
+// If larger than this threshold, it's treated as discontinuity.
+static const int64_t kAnchorFluctuationAllowedUs = 10000ll;
+
 MediaClock::MediaClock()
     : mAnchorTimeMediaUs(-1),
       mAnchorTimeRealUs(-1),
@@ -64,9 +68,20 @@
         ALOGW("reject anchor time since it leads to negative media time.");
         return;
     }
+
+    if (maxTimeMediaUs != -1) {
+        mMaxTimeMediaUs = maxTimeMediaUs;
+    }
+    if (mAnchorTimeRealUs != -1) {
+        int64_t oldNowMediaUs =
+            mAnchorTimeMediaUs + (nowUs - mAnchorTimeRealUs) * (double)mPlaybackRate;
+        if (nowMediaUs < oldNowMediaUs
+                && nowMediaUs > oldNowMediaUs - kAnchorFluctuationAllowedUs) {
+            return;
+        }
+    }
     mAnchorTimeRealUs = nowUs;
     mAnchorTimeMediaUs = nowMediaUs;
-    mMaxTimeMediaUs = maxTimeMediaUs;
 }
 
 void MediaClock::updateMaxTimeMedia(int64_t maxTimeMediaUs) {