[GStreamer] Ignore sinks position while seeking

https://bugs.webkit.org/show_bug.cgi?id=272167

Reviewed by Alicia Boya Garcia.

After removing MSE data, sinks get flushed and are not able to return
valid playback time. Some implementation return invalid time, 0.00 or
even some random value. This value may be then reported up to
HTMLMediaElement and that may be confusing to web applications.

This commit doesn't trust sinks position when pipeline is not prerolled,
as behavor is different across devices. The last cached position is used
instead.

To reflect better what's actually happening, isPipelineSeeking() has been
renamed as isPipelineWaitingPreroll() and the condition now also includes
pending states higher than paused.

Original author: Andrzej Surdej (https://github.com/asurdej-comcast)

See: #1302

* Source/WebCore/platform/graphics/gstreamer/MediaPlayerPrivateGStreamer.cpp:
(WebCore::MediaPlayerPrivateGStreamer::isPipelineWaitingPreroll const): Renamed from isPipelineSeeking().
(WebCore::MediaPlayerPrivateGStreamer::play): isPipelineSeeking() now named as isPipelineWaitingPreroll().
(WebCore::MediaPlayerPrivateGStreamer::paused const): Ditto.
(WebCore::MediaPlayerPrivateGStreamer::changePipelineState): Ditto.
(WebCore::MediaPlayerPrivateGStreamer::playbackPosition const): Use GST_CLOCK_TIME_NONE when the pipeline isn't prerolled. This will force the usage of the target seek time (if possible) or the last cached position (in the worst case).
(WebCore::MediaPlayerPrivateGStreamer::isPipelineSeeking const): Deleted. Renamed to isPipelineWaitingPreroll().
* Source/WebCore/platform/graphics/gstreamer/MediaPlayerPrivateGStreamer.h: isPipelineSeeking() now named as isPipelineWaitingPreroll().
* Source/WebCore/platform/graphics/gstreamer/mse/MediaPlayerPrivateGStreamerMSE.cpp:
(WebCore::MediaPlayerPrivateGStreamerMSE::updateStates): isPipelineSeeking() now named as isPipelineWaitingPreroll().

Canonical link: https://commits.webkit.org/277541@main

Author: asurdej-comcast

Source/WebCore/platform/graphics/gstreamer/MediaPlayerPrivateGStreamer.cpp

@@ -410,16 +410,16 @@ void MediaPlayerPrivateGStreamer::prepareToPlay()
     }
 }
 
-bool MediaPlayerPrivateGStreamer::isPipelineSeeking(GstState current, GstState pending, GstStateChangeReturn change) const
+bool MediaPlayerPrivateGStreamer::isPipelineWaitingPreroll(GstState current, GstState pending, GstStateChangeReturn change) const
 {
-    return change == GST_STATE_CHANGE_ASYNC && current == GST_STATE_PAUSED && pending == GST_STATE_PAUSED;
+    return change == GST_STATE_CHANGE_ASYNC && current == GST_STATE_PAUSED && pending >= GST_STATE_PAUSED;
 }
 
-bool MediaPlayerPrivateGStreamer::isPipelineSeeking() const
+bool MediaPlayerPrivateGStreamer::isPipelineWaitingPreroll() const
 {
     GstState current, pending;
     GstStateChangeReturn change = gst_element_get_state(m_pipeline.get(), &current, &pending, 0);
-    return isPipelineSeeking(current, pending, change);
+    return isPipelineWaitingPreroll(current, pending, change);
 }
 
 void MediaPlayerPrivateGStreamer::play()
@@ -436,7 +436,7 @@ void MediaPlayerPrivateGStreamer::play()
         return;
     }
 
-    if (isPipelineSeeking()) {
+    if (isPipelineWaitingPreroll()) {
         GST_DEBUG_OBJECT(pipeline(), "pipeline is seeking, let's delay moving the pipeline to playing right now");
         return;
     }
@@ -497,7 +497,7 @@ bool MediaPlayerPrivateGStreamer::paused() const
         return isPipelinePaused;
 
 #if !defined(GST_DISABLE_GST_DEBUG) || !defined(NDEBUG)
-    if (!isPipelineSeeking(state, pending, stateChange) && isPipelinePaused != !m_isPipelinePlaying
+    if (!isPipelineWaitingPreroll(state, pending, stateChange) && isPipelinePaused != !m_isPipelinePlaying
         && (stateChange == GST_STATE_CHANGE_SUCCESS || stateChange == GST_STATE_CHANGE_NO_PREROLL)) {
         GST_WARNING_OBJECT(pipeline(), "states are not synchronized, player paused %s, pipeline paused %s",
             boolForPrinting(!m_isPipelinePlaying), boolForPrinting(isPipelinePaused));
@@ -978,7 +978,7 @@ MediaPlayerPrivateGStreamer::ChangePipelineStateResult MediaPlayerPrivateGStream
 
     GstState currentState, pending;
     GstStateChangeReturn change = gst_element_get_state(m_pipeline.get(), &currentState, &pending, 0);
-    if (isPipelineSeeking(currentState, pending, change)) {
+    if (isPipelineWaitingPreroll(currentState, pending, change)) {
         GST_DEBUG_OBJECT(pipeline(), "rejected state change during seek");
         return ChangePipelineStateResult::Rejected;
     }
@@ -1402,7 +1402,8 @@ MediaTime MediaPlayerPrivateGStreamer::playbackPosition() const
         return m_cachedPosition;
     }
 
-    GstClockTime gstreamerPosition = gstreamerPositionFromSinks();
+    // We can't trust sinks position when pipeline is flushed (e.g. after MSE samples removal).
+    GstClockTime gstreamerPosition = isPipelineWaitingPreroll() ? GST_CLOCK_TIME_NONE : gstreamerPositionFromSinks();
     GST_TRACE_OBJECT(pipeline(), "Position %" GST_TIME_FORMAT ", canFallBackToLastFinishedSeekPosition: %s", GST_TIME_ARGS(gstreamerPosition), boolForPrinting(m_canFallBackToLastFinishedSeekPosition));
 
     // Cached position is marked as non valid here but we might fail to get a new one so initializing to this as "educated guess".

Source/WebCore/platform/graphics/gstreamer/MediaPlayerPrivateGStreamer.h

@@ -377,8 +377,8 @@ class MediaPlayerPrivateGStreamer : public MediaPlayerPrivateInterface
 
     void setCachedPosition(const MediaTime&) const;
 
-    bool isPipelineSeeking(GstState current, GstState pending, GstStateChangeReturn) const;
-    bool isPipelineSeeking() const;
+    bool isPipelineWaitingPreroll(GstState current, GstState pending, GstStateChangeReturn) const;
+    bool isPipelineWaitingPreroll() const;
 
     Ref<MainThreadNotifier<MainThreadNotification>> m_notifier;
     MediaPlayer* m_player;

Source/WebCore/platform/graphics/gstreamer/mse/MediaPlayerPrivateGStreamerMSE.cpp

@@ -386,7 +386,7 @@ void MediaPlayerPrivateGStreamerMSE::sourceSetup(GstElement* sourceElement)
 
 void MediaPlayerPrivateGStreamerMSE::updateStates()
 {
-    bool isSeeking = isPipelineSeeking();
+    bool isSeeking = isPipelineWaitingPreroll();
     bool shouldBePlaying = (!m_isPaused && readyState() >= MediaPlayer::ReadyState::HaveFutureData && m_playbackRatePausedState != PlaybackRatePausedState::RatePaused)
         || m_playbackRatePausedState == PlaybackRatePausedState::ShouldMoveToPlaying;
     GST_DEBUG_OBJECT(pipeline(), "shouldBePlaying = %s, m_isPipelinePlaying = %s, is seeking %s", boolForPrinting(shouldBePlaying),