Implement evictFrames() to support MSE's coded frame eviction algorithm.

media/filters/source_buffer_stream.cc

Index: media/filters/source_buffer_stream.cc
diff --git a/media/filters/source_buffer_stream.cc b/media/filters/source_buffer_stream.cc
index faba8ec9d1e8d75832cd3ce30296e4c7b766397a..be6594a334c6b3b7fb17a9fe9a370736d716deb0 100644
--- a/media/filters/source_buffer_stream.cc
+++ b/media/filters/source_buffer_stream.cc
@@ -348,8 +348,6 @@ bool SourceBufferStream::Append(const BufferQueue& buffers) {
 
   SetSelectedRangeIfNeeded(next_buffer_timestamp);
 
-  GarbageCollectIfNeeded();
-
   DVLOG(1) << __FUNCTION__ << " " << GetStreamTypeName()
            << ": done. ranges_=" << RangesToString(ranges_);
   DCHECK(IsRangeListSorted(ranges_));
@@ -583,7 +581,7 @@ void SourceBufferStream::SetConfigIds(const BufferQueue& buffers) {
   }
 }
 
-void SourceBufferStream::GarbageCollectIfNeeded() {
+bool SourceBufferStream::GarbageCollectIfNeeded(DecodeTimestamp media_time) {
   // Compute size of |ranges_|.
   int ranges_size = 0;
   for (RangeList::iterator itr = ranges_.begin(); itr != ranges_.end(); ++itr)
@@ -591,7 +589,7 @@ void SourceBufferStream::GarbageCollectIfNeeded() {
 
   // Return if we're under or at the memory limit.
   if (ranges_size <= memory_limit_)
-    return;
+    return true;
 
   int bytes_to_free = ranges_size - memory_limit_;
 
@@ -605,15 +603,13 @@ void SourceBufferStream::GarbageCollectIfNeeded() {
 
   // Begin deleting from the front.
   if (bytes_to_free - bytes_freed > 0)
-    bytes_freed += FreeBuffers(bytes_to_free - bytes_freed, false);
-
-  // Begin deleting from the back.
-  if (bytes_to_free - bytes_freed > 0)
-    bytes_freed += FreeBuffers(bytes_to_free - bytes_freed, true);

[servolk, 2014/12/12 01:01:53]

So now we are never gonna to try freeing buffers from the back? Is it safe? What
if we are playing at the end of a very long video and then seek back to
beginning. I think in the past GC would remove the buffers at the back of the
SBS - how is it gonna be handled now?

[kjoswiak, 2014/12/12 01:22:05]

The call to FreeBuffersAfterLastAppended on line 604 should take care of extra
buffers at end of our ranges.

This call removes buffers between current playhead and last append, which is
going to create a gap in the buffer. This is the source of gaps that have been
causing the playback stall bugs, since most clients are not going to expect
they're going to have to reappend data in this range.

I can put this call back in if I'm misunderstanding the situation, but I think
this is the source of GC over aggression, and would prefer we fail rather than
try this call.

+    bytes_freed += FreeBuffers(bytes_to_free - bytes_freed, media_time, false);
 
   DVLOG(2) << __FUNCTION__ << " " << GetStreamTypeName() << ": After GC"
            << " bytes_freed=" << bytes_freed
            << " ranges_=" << RangesToString(ranges_);
+
+  return (bytes_to_free - bytes_freed <= 0);

[servolk, 2014/12/12 01:01:53]

Why not just "return bytes_freed >= bytes_to_free" ? I think that would be more
readable.

[kjoswiak, 2014/12/12 01:22:05]

Done.

 }
 
 int SourceBufferStream::FreeBuffersAfterLastAppended(int total_bytes_to_free) {
@@ -676,6 +672,7 @@ int SourceBufferStream::GetRemovalRange(
 }
 
 int SourceBufferStream::FreeBuffers(int total_bytes_to_free,
+                                    DecodeTimestamp media_time,
                                     bool reverse_direction) {
   TRACE_EVENT2("media", "SourceBufferStream::FreeBuffers",
                "total bytes to free", total_bytes_to_free,
@@ -707,6 +704,10 @@ int SourceBufferStream::FreeBuffers(int total_bytes_to_free,
         DCHECK_EQ(current_range, selected_range_);
         break;
       }
+      if (media_time != kNoDecodeTimestamp() &&
+          !current_range->FirstGOPEarlierThanMediaTime(media_time)) {
+        break;
+      }
       bytes_deleted = current_range->DeleteGOPFromFront(&buffers);
     }