Improve HTMLMediaElement::currentTime()

third_party/WebKit/Source/modules/mediasource/SourceBuffer.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 1139 matching lines @@
     return false;
   }
 
   TRACE_EVENT_ASYNC_END0("media", "SourceBuffer::prepareAppend", this);
   return true;
 }
 
 bool SourceBuffer::evictCodedFrames(size_t newDataSize) {
   DCHECK(m_source);
   DCHECK(m_source->mediaElement());
+
+  // Nothing to do if the mediaElement does not yet have frames to evict.
+  // mediaElement()->currentTime() will be NaN.
+  if (m_source->mediaElement()->getReadyState() <
+      HTMLMediaElement::kHaveMetadata)
+    return true;

[mlamouri (slow - plz ping), 2016/10/26 15:32:54]

style: wrap in { }

Would it make sense to check for currentTime(0 ==
std::numeric_limits<double>quiet_NaN() instead of the ready state?

[chcunningham, 2016/10/26 19:29:41]

Done.
This NaN issue actually disappeared once I realized NaN was not the right value
to initialize official/current position to (now using 0). 

I still think this is a nice optimization, so I'll leave it. Checking readyState
is the right thing, since currentTime can be zero irrespective of whether we
have data to consider evicting.

+
   double currentTime = m_source->mediaElement()->currentTime();
   bool result = m_webSourceBuffer->evictCodedFrames(currentTime, newDataSize);
   if (!result) {
     BLINK_SBLOG << __func__ << " this=" << this
                 << " failed. newDataSize=" << newDataSize
                 << " currentTime=" << currentTime << " buffered="
                 << webTimeRangesToString(m_webSourceBuffer->buffered());
   }
   return result;
 }
@@ skipping 316 matching lines @@
   visitor->trace(m_removeAsyncPartRunner);
   visitor->trace(m_appendStreamAsyncPartRunner);
   visitor->trace(m_stream);
   visitor->trace(m_audioTracks);
   visitor->trace(m_videoTracks);
   EventTargetWithInlineData::trace(visitor);
   ActiveDOMObject::trace(visitor);
 }
 
 }  // namespace blink