MSE: Experimental support for new abort and duration behavior

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

Index: third_party/WebKit/Source/modules/mediasource/MediaSource.cpp
diff --git a/third_party/WebKit/Source/modules/mediasource/MediaSource.cpp b/third_party/WebKit/Source/modules/mediasource/MediaSource.cpp
index 6ff989db99a5205db5e1e97c90d6dd2c29b5f8ce..71d93d77c745f2901ce5b430a4f9914a56cde8e3 100644
--- a/third_party/WebKit/Source/modules/mediasource/MediaSource.cpp
+++ b/third_party/WebKit/Source/modules/mediasource/MediaSource.cpp
@@ -36,6 +36,8 @@
 #include "core/dom/ExceptionCode.h"
 #include "core/events/Event.h"
 #include "core/events/GenericEventQueue.h"
+#include "core/frame/Deprecation.h"
+#include "core/frame/UseCounter.h"
 #include "core/html/HTMLMediaElement.h"
 #include "core/html/TimeRanges.h"
 #include "modules/mediasource/MediaSourceRegistry.h"
@@ -411,27 +413,49 @@ void MediaSource::setDuration(double duration, ExceptionState& exceptionState)
 
     // 4. Run the duration change algorithm with new duration set to the value being
     // assigned to this attribute.
-    durationChangeAlgorithm(duration);
+    durationChangeAlgorithm(duration, exceptionState);
 }
 
-void MediaSource::durationChangeAlgorithm(double newDuration)
+void MediaSource::durationChangeAlgorithm(double newDuration, ExceptionState& exceptionState)
 {
-    // Section 2.6.4 Duration change
-    // https://dvcs.w3.org/hg/html-media/raw-file/default/media-source/media-source.html#duration-change-algorithm
+    // http://w3c.github.io/media-source/#duration-change-algorithm
     // 1. If the current value of duration is equal to new duration, then return.
     if (newDuration == duration())
         return;
 
-    // 2. Set old duration to the current value of duration.
+    // 2. If new duration is less than the highest starting presentation
+    // timestamp of any buffered coded frames for all SourceBuffer objects in
+    // sourceBuffers, then throw an InvalidStateError exception and abort these
+    // steps. Note: duration reductions that would truncate currently buffered
+    // media are disallowed. When truncation is necessary, use remove() to
+    // reduce the buffered range before updating duration.
+    double highestBufferedPresentationTimestamp = 0;
+    for (size_t i = 0; i < m_sourceBuffers->length(); ++i) {
+        highestBufferedPresentationTimestamp = std::max(highestBufferedPresentationTimestamp, m_sourceBuffers->item(i)->highestPresentationTimestamp());
+    }
+
+    if (newDuration < highestBufferedPresentationTimestamp) {
+        if (RuntimeEnabledFeatures::mediaSourceNewAbortAndDurationEnabled()) {
+            logAndThrowDOMException(exceptionState, InvalidStateError, "Setting duration below highest presentation timestamp of any buffered coded frames is disallowed. Instead, first do asynchronous remove(newDuration, oldDuration) on all sourceBuffers, where newDuration < oldDuration.");
+            return;
+        }
+
+        Deprecation::countDeprecation(m_attachedElement->document(), UseCounter::MediaSourceDurationTruncatingBuffered);
+        // See also deprecated remove(new duration, old duration) behavior below.

[chcunningham, 2016/06/29 21:19:24]

given that they aren't related, this is maybe more confusing than helpful (or
i'm missing something)

[wolenetz, 2016/06/30 01:35:49]

They are tightly related. This is referring to line 456. The new behavior
requires enforcement here, so deprecation warning is done here. The old behavior
(which is deprecated) is at line 456.

+    }
+
+    // 3. Set old duration to the current value of duration.
     double oldDuration = duration();
+    DCHECK_LE(highestBufferedPresentationTimestamp, oldDuration);
 
+    // 4. Update duration to new duration.
     bool requestSeek = m_attachedElement->currentTime() > newDuration;
-
-    // 3. Update duration to new duration.
     m_webMediaSource->setDuration(newDuration);
 
-    // 4. If the new duration is less than old duration, then call remove(new duration, old duration) on all all objects in sourceBuffers.
-    if (newDuration < oldDuration) {
+    if (!RuntimeEnabledFeatures::mediaSourceNewAbortAndDurationEnabled() && newDuration < oldDuration) {

[chcunningham, 2016/06/29 21:19:24]

Maybe you can save some cycles and only run this remove call if newDuration <
highestPresTime. IIUC, running whenever highestPresTime < newDuration <
oldDuration is a no-op (other than firing a few events... which is perhaps
problematic for my proposal)

[wolenetz, 2016/06/30 01:35:49]

There are events and an async period of time when updating is held true.
Otherwise, you'd be correct. But we still need to do the old behavior (including
events and async scheduling of a no-op removal where highestPresTime <
newDuration < oldDuration during which time updating becomes true).

+        // Deprecated behavior: if the new duration is less than old duration,
+        // then call remove(new duration, old duration) on all all objects in
+        // sourceBuffers.
         for (size_t i = 0; i < m_sourceBuffers->length(); ++i)
             m_sourceBuffers->item(i)->remove(newDuration, oldDuration, ASSERT_NO_EXCEPTION);
     }