Bug 670055 - Seek video to exact audio sample. r=kinetik

content/media/nsBuiltinDecoderReader.cpp

@@ -310,6 +310,10 @@ nsresult nsBuiltinDecoderReader::DecodeToTarget(PRInt64 aTarget)
 
   if (HasAudio()) {
     // Decode audio forward to the seek target.
+    PRInt64 targetSample = 0;
+    if (!UsecsToSamples(aTarget, mInfo.mAudioRate, targetSample)) {
+      return NS_ERROR_FAILURE;
+    }
     PRBool eof = PR_FALSE;
     while (HasAudio() && !eof) {
       while (!eof && mAudioQueue.GetSize() == 0) {
@@ -322,14 +326,53 @@ nsresult nsBuiltinDecoderReader::DecodeToTarget(PRInt64 aTarget)
           }
         }
       }
-      nsAutoPtr<SoundData> audio(mAudioQueue.PeekFront());
-      if (audio && audio->mTime + audio->mDuration <= aTarget) {
-        mAudioQueue.PopFront();
+      const SoundData* audio = mAudioQueue.PeekFront();
+      if (!audio)
+        break;
+      PRInt64 startSample = 0;
+      if (!UsecsToSamples(audio->mTime, mInfo.mAudioRate, startSample)) {
+        return NS_ERROR_FAILURE;
+      }
+      if (startSample + audio->mSamples <= targetSample) {
+        // Our seek target lies after the samples in this SoundData. Pop it
+        // off the queue, and keep decoding forwards.
+        delete mAudioQueue.PopFront();
         audio = nsnull;
-      } else {
-        audio.forget();
+        continue;
+      }
+
+      // The seek target lies somewhere in this SoundData's samples, strip off
+      // any samples which lie before the seek target, so we'll begin playback
+      // exactly at the seek target.
+      NS_ASSERTION(targetSample >= startSample, "Target must at or be after data start.");
+      NS_ASSERTION(startSample + audio->mSamples > targetSample, "Data must end after target.");
+
+      PRInt64 samplesToPrune = targetSample - startSample;
+      if (samplesToPrune > audio->mSamples) {
+        // We've messed up somehow. Don't try to trim samples, the |samples|
+        // variable below will overflow.
+        NS_WARNING("Can't prune more samples that we have!");
         break;
       }
+      PRUint32 samples = audio->mSamples - static_cast<PRUint32>(samplesToPrune);
+      PRUint32 channels = audio->mChannels;
+      nsAutoArrayPtr<SoundDataValue> audioData(new SoundDataValue[samples * channels]);
+      memcpy(audioData.get(),
+             audio->mAudioData.get() + (samplesToPrune * channels),
+             samples * channels * sizeof(SoundDataValue));
+      PRInt64 duration;
+      if (!SamplesToUsecs(samples, mInfo.mAudioRate, duration)) {
+        return NS_ERROR_FAILURE;
+      }
+      nsAutoPtr<SoundData> data(new SoundData(audio->mOffset,
+                                              aTarget,
+                                              duration,
+                                              samples,
+                                              audioData.forget(),
+                                              channels));
+      delete mAudioQueue.PopFront();
+      mAudioQueue.PushFront(data.forget());
+      break;
     }
   }
   return NS_OK;