[GStreamer] Account for internal pauses because of buffering

https://bugs.webkit.org/show_bug.cgi?id=287881

Reviewed by Xabier Rodriguez-Calvar and Philippe Normand.

The PlaybackRatePausedState in MediaPlayerPrivateGStreamer only accounts
for different pause reasons because of manual pause and playbackRate ==
0, but pauses because of low buffering level should also be accounted.
Currently they aren't (but the player can get paused because of it) and
that's confusing the code that deals with pauses/unpauses because of
playbackRate.

See: #1455

This downstream PR proposes to "abuse"
PlaybackRatePausedState::RatePaused to keep tack of pauses because of
buffering, but that's conceptually wrong. A new BufferingPaused state
should be created to keep track of this pause reason and be able to
recover from it (unpause) later.

This commit creates that new BufferingPaused state and keeps track of
it in a similar way to how ManuallyPaused is managed (but pauses for
buffering aren't explicit manual pauses).

Co-authored by: suresh-khurdiya-infosys <skhurdiya.ext@libertyglobal.com>

* Source/WebCore/platform/graphics/gstreamer/MediaPlayerPrivateGStreamer.cpp:
(WebCore::MediaPlayerPrivateGStreamer::play): Also set RatePaused when we're in the BufferingPaused state and playbackRate is zero.
(WebCore::MediaPlayerPrivateGStreamer::updateStates): Set m_playbackRatePausedState to RatePaused when the rate is actually zero, and to BufferingPaused when the pause happens because of buffering.
* Source/WebCore/platform/graphics/gstreamer/MediaPlayerPrivateGStreamer.h: Added new PlaybackRatePausedState::BufferingPaused state and explanation.

Canonical link: https://commits.webkit.org/290606@main

Author: eocanha

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

@@ -434,7 +434,8 @@ void MediaPlayerPrivateGStreamer::play()
 
     if (!m_playbackRate) {
         if (m_playbackRatePausedState == PlaybackRatePausedState::InitiallyPaused
-            || m_playbackRatePausedState == PlaybackRatePausedState::ManuallyPaused)
+            || m_playbackRatePausedState == PlaybackRatePausedState::ManuallyPaused
+            || m_playbackRatePausedState == PlaybackRatePausedState::BufferingPaused)
             m_playbackRatePausedState = PlaybackRatePausedState::RatePaused;
         return;
     }
@@ -2620,8 +2621,13 @@ void MediaPlayerPrivateGStreamer::updateStates()
             m_isPaused = false;
 
             shouldPauseForBuffering = (!m_wasBuffering && m_isBuffering && !m_isLiveStream.value_or(false));
-            if (shouldPauseForBuffering || !m_playbackRate) {
-                GST_INFO_OBJECT(pipeline(), "[Buffering] Pausing stream for buffering or because of zero playback rate.");
+            if (!m_playbackRate) {
+                GST_INFO_OBJECT(pipeline(), "[Buffering] Pausing stream because of zero playback rate.");
+                m_playbackRatePausedState = PlaybackRatePausedState::RatePaused;
+                changePipelineState(GST_STATE_PAUSED);
+            } else if (shouldPauseForBuffering) {
+                GST_INFO_OBJECT(pipeline(), "[Buffering] Pausing stream for buffering.");
+                m_playbackRatePausedState = PlaybackRatePausedState::BufferingPaused;
                 changePipelineState(GST_STATE_PAUSED);
             }
         } else

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

@@ -313,6 +313,9 @@ class MediaPlayerPrivateGStreamer : public MediaPlayerPrivateInterface
         ManuallyPaused,
         // Pipeline was playing and rate was set to zero.
         RatePaused,
+        // Pipeline was playing and had to be paused for buffering reasons. This state is
+        // like ManuallyPaused, but not requested by the user.
+        BufferingPaused,
         // Pipeline was paused because of zero rate and it should be playing. This is not a
         // definitive state, just an operational transition from RatePaused to Playing to keep the
         // pipeline state changes contained in updateStates.