b=1016177 reduce MEDIA_TIME_MAX to not overflow when multiplying by sample rates r=roc

MediaTimes are multiplied by sample rates when converting to ticks.

This new maximum leaves 24 bits to count seconds, which corresponds to 194
days.

TimeVarying::GetAt() can return INT64_MAX, which may be > GRAPH_TIME_MAX.

The "Start time too early" assertion would now fail because conversion of
STREAM_TIME_MAX to ticks no longer overflows.

--HG--
extra : rebase_source : b49c95315d0c633f191ff68aab0b5b7aa04c6e38

content/media/MediaSegment.h

@@ -15,13 +15,23 @@
 
 namespace mozilla {
 
+/**
+ * Track rate in Hz. Maximum 1 << TRACK_RATE_MAX_BITS Hz. This
+ * maximum avoids overflow in conversions between track rates and conversions
+ * from seconds.
+ */
+typedef int32_t TrackRate;
+const int64_t TRACK_RATE_MAX_BITS = 20;
+const TrackRate TRACK_RATE_MAX = 1 << TRACK_RATE_MAX_BITS;
+
 /**
  * We represent media times in 64-bit fixed point. So 1 MediaTime is
- * 1/(2^MEDIA_TIME_FRAC_BITS) seconds.
+ * 1/(2^MEDIA_TIME_FRAC_BITS) seconds.  We want to make sure that multiplying
+ * MediaTime by a TrackRate doesn't overflow, so we set its max accordingly.
  */
 typedef int64_t MediaTime;
 const int64_t MEDIA_TIME_FRAC_BITS = 20;
-const int64_t MEDIA_TIME_MAX = INT64_MAX;
+const int64_t MEDIA_TIME_MAX = INT64_MAX >> TRACK_RATE_MAX_BITS;
 
 inline MediaTime MillisecondsToMediaTime(int32_t aMS)
 {

content/media/MediaStreamGraph.cpp

@@ -2517,7 +2517,7 @@ MediaInputPort::GetNextInputInterval(GraphTime aTime)
   for (;;) {
     if (!mDest->mBlocked.GetAt(t, &end))
       break;
-    if (end == GRAPH_TIME_MAX)
+    if (end >= GRAPH_TIME_MAX)
       return result;
     t = end;
   }

content/media/StreamBuffer.h

@@ -17,13 +17,6 @@ namespace mozilla {
 typedef MediaTime StreamTime;
 const StreamTime STREAM_TIME_MAX = MEDIA_TIME_MAX;
 
-/**
- * Track rate in Hz. Maximum 1 << MEDIA_TIME_FRAC_BITS Hz. This ensures
- * calculations below don't overflow.
- */
-typedef int32_t TrackRate;
-const TrackRate TRACK_RATE_MAX = 1 << MEDIA_TIME_FRAC_BITS;
-
 /**
  * Unique ID for track within a StreamBuffer. Tracks from different
  * StreamBuffers may have the same ID; this matters when appending StreamBuffers,
@@ -224,8 +217,14 @@ public:
    */
   Track& AddTrack(TrackID aID, TrackRate aRate, TrackTicks aStart, MediaSegment* aSegment)
   {
-    NS_ASSERTION(TimeToTicksRoundDown(aRate, mTracksKnownTime) <= aStart,
-                 "Start time too early");
+    if (mTracksKnownTime == STREAM_TIME_MAX) {
+      // There exists code like
+      // http://mxr.mozilla.org/mozilla-central/source/media/webrtc/signaling/src/mediapipeline/MediaPipeline.cpp?rev=96b197deb91e&mark=1292-1297#1292
+      NS_WARNING("Adding track to StreamBuffer that should have no more tracks");
+    } else {
+      NS_ASSERTION(TimeToTicksRoundDown(aRate, mTracksKnownTime) <= aStart,
+                   "Start time too early");
+    }
     NS_ASSERTION(!FindTrack(aID), "Track with this ID already exists");
 
     return **mTracks.InsertElementSorted(new Track(aID, aRate, aStart, aSegment),