[Video] MediaSession API event handlers can resume background video.

third_party/WebKit/Source/core/html/HTMLMediaElement.cpp

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 #include "core/html/HTMLMediaElement.h"
 
+#include <limits>
 #include "bindings/core/v8/ExceptionState.h"
 #include "bindings/core/v8/Microtask.h"
 #include "bindings/core/v8/ScriptController.h"
 #include "bindings/core/v8/ScriptEventListener.h"
 #include "bindings/core/v8/ScriptPromiseResolver.h"
 #include "core/HTMLNames.h"
 #include "core/css/MediaList.h"
 #include "core/dom/Attribute.h"
 #include "core/dom/DOMException.h"
+#include "core/dom/DocumentUserGestureToken.h"
 #include "core/dom/ElementTraversal.h"
 #include "core/dom/ElementVisibilityObserver.h"
 #include "core/dom/Fullscreen.h"
 #include "core/dom/TaskRunnerHelper.h"
 #include "core/dom/shadow/ShadowRoot.h"
 #include "core/events/Event.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/Settings.h"
 #include "core/frame/UseCounter.h"
@@ skipping 42 matching lines @@
 #include "public/platform/WebMediaPlayerSource.h"
 #include "public/platform/WebMediaStream.h"
 #include "public/platform/modules/remoteplayback/WebRemotePlaybackAvailability.h"
 #include "public/platform/modules/remoteplayback/WebRemotePlaybackClient.h"
 #include "public/platform/modules/remoteplayback/WebRemotePlaybackState.h"
 #include "wtf/AutoReset.h"
 #include "wtf/CurrentTime.h"
 #include "wtf/MathExtras.h"
 #include "wtf/PtrUtil.h"
 #include "wtf/text/CString.h"
-#include <limits>
 
 #ifndef BLINK_MEDIA_LOG
 #define BLINK_MEDIA_LOG DVLOG(3)
 #endif
 
 #ifndef LOG_MEDIA_EVENTS
 // Default to not logging events because so many are generated they can
 // overwhelm the rest of the logging.
 #define LOG_MEDIA_EVENTS 0
 #endif
@@ skipping 306 matching lines @@
       m_deferredLoadState(NotDeferred),
       m_deferredLoadTimer(this, &HTMLMediaElement::deferredLoadTimerFired),
       m_webLayer(nullptr),
       m_displayMode(Unknown),
       m_officialPlaybackPosition(0),
       m_officialPlaybackPositionNeedsUpdate(true),
       m_fragmentEndTime(std::numeric_limits<double>::quiet_NaN()),
       m_pendingActionFlags(0),
       m_lockedPendingUserGesture(false),
       m_lockedPendingUserGestureIfCrossOriginExperimentEnabled(true),
+      m_wasLockedWhenBackgrounded(false),
       m_playing(false),
       m_shouldDelayLoadEvent(false),
       m_haveFiredLoadedData(false),
       m_canAutoplay(true),
       m_muted(false),
       m_paused(true),
       m_seeking(false),
       m_sentStalledEvent(false),
       m_ignorePreloadNone(false),
       m_textTracksVisible(false),
@@ skipping 1871 matching lines @@
 
   setIgnorePreloadNone();
   updatePlayState();
 }
 
 void HTMLMediaElement::pause() {
   BLINK_MEDIA_LOG << "pause(" << (void*)this << ")";
 
   // Only buffer aggressively on a user-initiated pause. Other types of pauses
   // (which go directly to pauseInternal()) should not cause this behavior.
-  if (webMediaPlayer() && UserGestureIndicator::utilizeUserGesture())
+  if (webMediaPlayer() && UserGestureIndicator::utilizeUserGesture()) {
     webMediaPlayer()->setBufferingStrategy(
         WebMediaPlayer::BufferingStrategy::Aggressive);
+  }
 
   if (m_autoplayVisibilityObserver) {
     m_autoplayVisibilityObserver->stop();
     m_autoplayVisibilityObserver = nullptr;
   }
 
   pauseInternal();
 }
 
 void HTMLMediaElement::pauseInternal() {
@@ skipping 782 matching lines @@
   if (requestSeek)
     seek(duration);
 }
 
 void HTMLMediaElement::playbackStateChanged() {
   BLINK_MEDIA_LOG << "playbackStateChanged(" << (void*)this << ")";
 
   if (!webMediaPlayer())
     return;
 
+  // playbackStateChanged() is always a result of a user gesture.
+  UserGestureIndicator gestureIndicator(
+      DocumentUserGestureToken::create(&document()));
   if (webMediaPlayer()->paused())
-    pauseInternal();
+    pause();
   else
-    playInternal();
+    play();
 }

[mlamouri (slow - plz ping), 2017/02/20 12:00:17]

I know you already replied to this comment but this change will have a side
effect on other callers (such as WebMediaPlayerCast). Would it make sense to use
WebScopedUserGesture in WebMediaPlayerImpl?

[whywhat, 2017/02/20 17:16:04]

If I understood Dan correctly - in general, no :)
How will this affect other callers exactly?
I'm not sure the Cast notification call DelegateOnPlay/Pause. It calls
playbackStateChanged when switching back from the remote to local player to
continue local playback. I don't think it's broken.
I think ideally, instead of choosing whether to use MediaSession handler or the
renderer webmediaplayer delegate path, play/pause command should always come
through HTMLMediaElement. Doing it in this change will make it too big though :/

 
 void HTMLMediaElement::requestSeek(double time) {
   // The player is the source of this seek request.
   setCurrentTime(time);
 }
 
 void HTMLMediaElement::remoteRouteAvailabilityChanged(
     WebRemotePlaybackAvailability availability) {
   if (remotePlaybackClient())
     remotePlaybackClient()->availabilityChanged(availability);
@@ skipping 40 matching lines @@
 void HTMLMediaElement::cancelledRemotePlaybackRequest() {
   if (remotePlaybackClient())
     remotePlaybackClient()->promptCancelled();
 }
 
 void HTMLMediaElement::remotePlaybackStarted() {
   if (remotePlaybackClient())
     remotePlaybackClient()->stateChanged(WebRemotePlaybackState::Connected);
 }
 
+void HTMLMediaElement::wasPausedWhenBackgrounded() {
+  // Prevent websites from resuming elements paused when backgrounded if
+  // user gesture is required for playback.
+  m_wasLockedWhenBackgrounded = m_lockedPendingUserGesture;
+  m_lockedPendingUserGesture = computeLockedPendingUserGesture(document());
+}
+
+void HTMLMediaElement::wasResumedWhenForegrounded() {
+  // If the element was resumed when foregrounded, restore its unlocked state.
+  if (m_lockedPendingUserGesture && !m_wasLockedWhenBackgrounded)
+    m_lockedPendingUserGesture = false;
+}

[mlamouri (slow - plz ping), 2017/02/20 12:00:17]

Instead of this logic, would it make sense if the autoplay checks (I guess
isLockedPendingUserGesture()) would check whether the video is visible and
require a user gesture if it is not. Does that make sense? Obviously, we would
need to reproduce some of the checks currently in WebMediaPlayerImpl in HTMLME
but that's the direction we want to take anyway, right?

[whywhat, 2017/02/20 17:16:04]

It should only require a user gesture until it's unlocked in the background and
before it's foregrounded again. So it would require a boolean bit anyhow.
It would also need to know whether the player has to be paused when hidden -
we'd have to expose ShouldPauseWhenHidden from WMPI (as we check for audio/video
only, keyframe distance, remote, etc).

+
 bool HTMLMediaElement::hasSelectedVideoTrack() {
   DCHECK(RuntimeEnabledFeatures::backgroundVideoTrackOptimizationEnabled());
 
   return m_videoTracks && m_videoTracks->selectedIndex() != -1;
 }
 
 WebMediaPlayer::TrackId HTMLMediaElement::getSelectedVideoTrackId() {
   DCHECK(RuntimeEnabledFeatures::backgroundVideoTrackOptimizationEnabled());
   DCHECK(hasSelectedVideoTrack());
 
   int selectedTrackIndex = m_videoTracks->selectedIndex();
   VideoTrack* track = m_videoTracks->anonymousIndexedGetter(selectedTrackIndex);
   return track->id();
 }
 
 bool HTMLMediaElement::isAutoplayingMuted() {
   if (!isHTMLVideoElement() ||
       !RuntimeEnabledFeatures::autoplayMutedVideosEnabled()) {
     return false;
   }
 
   return !paused() && muted() && isLockedPendingUserGesture();
 }
 
+bool HTMLMediaElement::isBackgroundVideoPlaybackUnlocked() {
+  return !isLockedPendingUserGesture();
+}
+
 void HTMLMediaElement::requestReload(const WebURL& newUrl) {
   DCHECK(webMediaPlayer());
   DCHECK(!m_srcObject);
   DCHECK(newUrl.isValid());
   DCHECK(isSafeToLoadURL(newUrl, Complain));
   resetMediaPlayerAndMediaSource();
   startPlayerLoad(newUrl);
 }
 
 // MediaPlayerPresentation methods
@@ skipping 624 matching lines @@
 bool HTMLMediaElement::isLockedPendingUserGesture() const {
   return m_lockedPendingUserGesture;
 }
 
 void HTMLMediaElement::unlockUserGesture() {
   m_lockedPendingUserGesture = false;
   m_lockedPendingUserGestureIfCrossOriginExperimentEnabled = false;
 }
 
 bool HTMLMediaElement::isGestureNeededForPlayback() const {
-  if (!m_lockedPendingUserGesture)
+  if (!isLockedPendingUserGesture())
     return false;
 
   return isGestureNeededForPlaybackIfPendingUserGestureIsLocked();
 }
 
 bool HTMLMediaElement::
     isGestureNeededForPlaybackIfCrossOriginExperimentEnabled() const {
   if (!m_lockedPendingUserGestureIfCrossOriginExperimentEnabled)
     return false;
 
@@ skipping 281 matching lines @@
       kMostlyFillViewportBecomeStableSeconds, BLINK_FROM_HERE);
 }
 
 void HTMLMediaElement::viewportFillDebouncerTimerFired(TimerBase*) {
   m_mostlyFillingViewport = true;
   if (m_webMediaPlayer)
     m_webMediaPlayer->becameDominantVisibleContent(m_mostlyFillingViewport);
 }
 
 }  // namespace blink