Add support for HTMLMediaElement::getStartDate()

Source/core/html/HTMLMediaElement.cpp

Index: Source/core/html/HTMLMediaElement.cpp
diff --git a/Source/core/html/HTMLMediaElement.cpp b/Source/core/html/HTMLMediaElement.cpp
index d5095be123ec94c9de987eebce36db2928a6ed73..1b70f84390926b0d47217d88bb4721f7e86b4577 100644
--- a/Source/core/html/HTMLMediaElement.cpp
+++ b/Source/core/html/HTMLMediaElement.cpp
@@ -251,6 +251,7 @@ HTMLMediaElement::HTMLMediaElement(const QualifiedName& tagName, Document& docum
     , m_lastSeekTime(0)
     , m_previousProgressTime(numeric_limits<double>::max())
     , m_duration(numeric_limits<double>::quiet_NaN())
+    , m_timelineOffset(numeric_limits<double>::quiet_NaN())
     , m_lastTimeUpdateEventWallTime(0)
     , m_lastTimeUpdateEventMovieTime(numeric_limits<double>::max())
     , m_loadState(WaitingForSource)
@@ -676,6 +677,8 @@ void HTMLMediaElement::prepareForLoad()
         invalidateCachedTime();
 
         // 4.9 - Set the timeline offset to Not-a-Number (NaN).
+        m_timelineOffset = numeric_limits<double>::quiet_NaN();
+
         // 4.10 - Update the duration attribute to Not-a-Number (NaN).
 
 
@@ -1602,11 +1605,32 @@ void HTMLMediaElement::setReadyState(MediaPlayer::ReadyState state)
     }
 
     if (m_readyState >= HAVE_METADATA && oldState < HAVE_METADATA) {
+        // This block corresponds to the "Once enough of the media data has been fetched to determine the duration of the media resource, its dimensions, and other metadata"
+        // section of step 4 of the resource fetch algorithm.
+
+        // FIXME: This appears to correspond to step 10 in the algorithm. Investigate moving this code to a position that matches the spec text.
         prepareMediaFragmentURI();
+
+        // 1. Establish the media timeline for the purposes of the current playback position, the earliest possible position, and the initial playback position, based on the media data.
+        // 2. Update the timeline offset to the date and time that corresponds to the zero time in the media timeline established in the previous step, if any. If no explicit time and date is given by the media resource, the timeline offset must be set to Not-a-Number (NaN).

[philipj_slow, 2014/05/06 11:13:52]

Nit: this is a very long line. There isn't a lot of consistency, but many spec
comments seem to be limited to 100 columns, so that would work.

+        m_timelineOffset = webMediaPlayer()->timelineOffset();
+
+        // 3. Set the current playback position and the official playback position to the earliest possible position.
+
+        // 4. Update the duration attribute with the time of the last frame of the resource, if known, on the media timeline established above. If it is not known (e.g. a stream that is in principle infinite), update the duration attribute to the value positive Infinity.
         scheduleEvent(EventTypeNames::durationchange);
+
+        // 5. For video elements, set the videoWidth and videoHeight attributes, and queue a task to fire a simple event named resize at the media element.
         if (isHTMLVideoElement(*this))
             scheduleEvent(EventTypeNames::resize);
+
+        // 6. Set the readyState attribute to HAVE_METADATA.
+        //   Note: A loadedmetadata DOM event will be fired as part of setting the readyState attribute to a new value.
         scheduleEvent(EventTypeNames::loadedmetadata);
+
+        // Steps 7-12 appear to be handled elsewhere.
+        // FIXME: Code should be refactored to make it easier to verify that these steps are implemented according to spec.
+
         if (hasMediaControls())
             mediaControls()->reset();
         if (renderer())
@@ -1914,6 +1938,11 @@ double HTMLMediaElement::duration() const
     return m_player->duration();
 }
 
+double HTMLMediaElement::getStartDate()
+{
+    return m_timelineOffset;

[philipj_slow, 2014/05/15 11:38:00]

My colleague has noticed that this value will be wrapped in a Date directly, so
it needs to be multiplied by 1000, probably here.

[acolwell GONE FROM CHROMIUM, 2014/05/15 13:01:22]

It is already supposed to be in milliseconds since
WebMediaPlayer::timelineOffset() that base::Time::ToJsTime() should be used to
generate this value. I've made a note to update the documentation on
m_timelineOffset.

[philipj_slow, 2014/05/15 13:28:29]

Thanks!

+}
+
 bool HTMLMediaElement::paused() const
 {
     return m_paused;