MSE: Experimental support for new abort and duration behavior

third_party/WebKit/Source/modules/mediasource/MediaSource.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 18 matching lines @@
  */
 
 #include "modules/mediasource/MediaSource.h"
 
 #include "bindings/core/v8/ExceptionMessages.h"
 #include "bindings/core/v8/ExceptionState.h"
 #include "bindings/core/v8/ExceptionStatePlaceholder.h"
 #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"
 #include "platform/ContentType.h"
 #include "platform/Logging.h"
 #include "platform/MIMETypeRegistry.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/TraceEvent.h"
 #include "public/platform/WebMediaSource.h"
 #include "public/platform/WebSourceBuffer.h"
@@ skipping 355 matching lines @@
 
     // 2. If the readyState attribute is not "open" then throw an InvalidStateError
     // exception and abort these steps.
     // 3. If the updating attribute equals true on any SourceBuffer in sourceBuffers,
     // then throw an InvalidStateError exception and abort these steps.
     if (throwExceptionIfClosedOrUpdating(isOpen(), isUpdating(), exceptionState))
         return;
 
     // 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);
     }
 
     // 5. If a user agent is unable to partially render audio frames or text cues that start before and end after the duration, then run the following steps:
     // NOTE: Currently we assume that the media engine is able to render partial frames/cues. If a media
     // engine gets added that doesn't support this, then we'll need to add logic to handle the substeps.
 
     // 6. Update the media controller duration to new duration and run the HTMLMediaElement duration change algorithm.
     m_attachedElement->durationChanged(newDuration, requestSeek);
@@ skipping 171 matching lines @@
 
     m_asyncEventQueue->enqueueEvent(event);
 }
 
 URLRegistry& MediaSource::registry() const
 {
     return MediaSourceRegistry::registry();
 }
 
 } // namespace blink