Bug 1440040 - Don't round up to next block unless necessary. r=padenot

With block size 128, rounding `128` to end of next block gives `256`, which is
not what we want when running MSG iterations. That could mean over-iterating and
buffering unnecessary amounts of silence.

MozReview-Commit-ID: vW14l2ygRy

--HG--
extra : rebase_source : 8aeedc8958e646f9730c9163447e3355a73fd42e

dom/media/GraphDriver.cpp

@@ -295,7 +295,7 @@ ThreadedDriver::RunThread()
     }
 
     GraphTime nextStateComputedTime =
-      mGraphImpl->RoundUpToNextAudioBlock(
+      mGraphImpl->RoundUpToEndOfAudioBlock(
         mIterationEnd + mGraphImpl->MillisecondsToMediaTime(AUDIO_TARGET_MS));
     if (nextStateComputedTime < stateComputedTime) {
       // A previous driver may have been processing further ahead of
@@ -923,7 +923,8 @@ AudioCallbackDriver::DataCallback(const AudioDataValue* aInputBuffer,
   // compute the iteration start and end from there, trying to keep the amount
   // of buffering in the graph constant.
   GraphTime nextStateComputedTime =
-    mGraphImpl->RoundUpToNextAudioBlock(stateComputedTime + mBuffer.Available());
+    mGraphImpl->RoundUpToEndOfAudioBlock(
+      stateComputedTime + mBuffer.Available());
 
   mIterationStart = mIterationEnd;
   // inGraph is the number of audio frames there is between the state time and

dom/media/MediaStreamGraph.cpp

@@ -1051,14 +1051,22 @@ MediaStreamGraphImpl::PrepareUpdatesToMainThreadState(bool aFinalUpdate)
   }
 }
 
+GraphTime
+MediaStreamGraphImpl::RoundUpToEndOfAudioBlock(GraphTime aTime)
+{
+  if (aTime % WEBAUDIO_BLOCK_SIZE == 0) {
+    return aTime;
+  }
+  return RoundUpToNextAudioBlock(aTime);
+}
+
 GraphTime
 MediaStreamGraphImpl::RoundUpToNextAudioBlock(GraphTime aTime)
 {
-  StreamTime ticks = aTime;
-  uint64_t block = ticks >> WEBAUDIO_BLOCK_SIZE_BITS;
+  uint64_t block = aTime >> WEBAUDIO_BLOCK_SIZE_BITS;
   uint64_t nextBlock = block + 1;
-  StreamTime nextTicks = nextBlock << WEBAUDIO_BLOCK_SIZE_BITS;
-  return nextTicks;
+  GraphTime nextTime = nextBlock << WEBAUDIO_BLOCK_SIZE_BITS;
+  return nextTime;
 }
 
 void
@@ -4243,8 +4251,8 @@ MediaStreamGraph::StartNonRealtimeProcessing(uint32_t aTicksToProcess)
     return;
 
   graph->mEndTime =
-    graph->RoundUpToNextAudioBlock(graph->mStateComputedTime +
-                                   aTicksToProcess - 1);
+    graph->RoundUpToEndOfAudioBlock(graph->mStateComputedTime +
+                                    aTicksToProcess);
   graph->mNonRealtimeProcessing = true;
   graph->EnsureRunInStableState();
 }

dom/media/MediaStreamGraphImpl.h

@@ -333,6 +333,11 @@ public:
    */
   void UpdateStreamOrder();
 
+  /**
+   * Returns smallest value of t such that t is a multiple of
+   * WEBAUDIO_BLOCK_SIZE and t >= aTime.
+   */
+  GraphTime RoundUpToEndOfAudioBlock(GraphTime aTime);
   /**
    * Returns smallest value of t such that t is a multiple of
    * WEBAUDIO_BLOCK_SIZE and t > aTime.