Enable round-tripping and updating of SourceBuffer timestamp offset

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 465 matching lines @@
 void SourceBuffer::scheduleEvent(const AtomicString& eventName)
 {
     ASSERT(m_asyncEventQueue);
 
     RefPtr<Event> event = Event::create(eventName);
     event->setTarget(this);
 
     m_asyncEventQueue->enqueueEvent(event.release());
 }
 
+void SourceBuffer::appendAndUpdateTimestampOffset(const unsigned char* data, unsigned length)
+{
+    double newTimestampOffset;

[jamesr, 2014/02/27 01:49:56]

this value is completely unininitialized

[wolenetz, 2014/02/27 03:29:58]

Done.

+    if (m_webSourceBuffer->append(data, length, &newTimestampOffset))
+        m_timestampOffset = newTimestampOffset;

[jamesr, 2014/02/27 01:49:56]

so if it's used here (i.e. the append() function returns true without actually
writing a value), we'll get completely undefined bits in here. any reason not to
initialize the local to something obvious like 0.0 on line 488?

[wolenetz, 2014/02/27 03:29:58]

Done.

+}
+
 void SourceBuffer::appendBufferInternal(const unsigned char* data, unsigned size, ExceptionState& exceptionState)
 {
     // Section 3.2 appendBuffer()
     // https://dvcs.w3.org/hg/html-media/raw-file/default/media-source/media-source.html#widl-SourceBuffer-appendBuffer-void-ArrayBufferView-data
 
     // Step 1 is enforced by the caller.
     // 2. If this object has been removed from the sourceBuffers attribute of the parent media source then throw an InvalidStateError exception and abort these steps.
     // 3. If the updating attribute equals true, then throw an InvalidStateError exception and abort these steps.
     if (throwExceptionIfRemovedOrUpdating(isRemoved(), m_updating, exceptionState))
         return;
@@ skipping 31 matching lines @@
 
     // 1. Run the segment parser loop algorithm.
     // Step 2 doesn't apply since we run Step 1 synchronously here.
     size_t appendSize = m_pendingAppendData.size();
     if (!appendSize) {
         // Resize buffer for 0 byte appends so we always have a valid pointer.
         // We need to convey all appends, even 0 byte ones to |m_webSourceBuffer|
         // so that it can clear its end of stream state if necessary.
         m_pendingAppendData.resize(1);
     }
-    m_webSourceBuffer->append(m_pendingAppendData.data(), appendSize);
+    appendAndUpdateTimestampOffset(m_pendingAppendData.data(), appendSize);
 
     // 3. Set the updating attribute to false.
     m_updating = false;
     m_pendingAppendData.clear();
 
     // 4. Queue a task to fire a simple event named update at this SourceBuffer object.
     scheduleEvent(EventTypeNames::update);
 
     // 5. Queue a task to fire a simple event named updateend at this SourceBuffer object.
     scheduleEvent(EventTypeNames::updateend);
@@ skipping 134 matching lines @@
 {
     WTF_LOG(Media, "SourceBuffer::didStartLoading() %p", this);
 }
 
 void SourceBuffer::didReceiveDataForClient(const char* data, unsigned dataLength)
 {
     WTF_LOG(Media, "SourceBuffer::didReceiveDataForClient(%d) %p", dataLength, this);
     ASSERT(m_updating);
     ASSERT(m_loader);
 
-    m_webSourceBuffer->append(reinterpret_cast<const unsigned char*>(data), dataLength);
+    appendAndUpdateTimestampOffset(reinterpret_cast<const unsigned char*>(data), dataLength);
 }
 
 void SourceBuffer::didFinishLoading()
 {
     WTF_LOG(Media, "SourceBuffer::didFinishLoading() %p", this);
     appendStreamDone(true);
 }
 
 void SourceBuffer::didFail(FileError::ErrorCode errorCode)
 {
     WTF_LOG(Media, "SourceBuffer::didFail(%d) %p", errorCode, this);
     appendStreamDone(false);
 }
 
 void SourceBuffer::trace(Visitor* visitor)
 {
     visitor->trace(m_source);
 }
 
 } // namespace WebCore