Improve GStreamer frame stepping reliability

internal/player/gstreamer_player.go

@@ -134,10 +134,18 @@ func (p *GStreamerPlayer) Load(path string, offset time.Duration) error {
 	}
 	C.free(unsafe.Pointer(syncName))
 	maxBuffers := C.CString("max-buffers")
-	C.vt_gst_set_int(appsink, maxBuffers, C.gint(2))
+	if p.preview {
+		C.vt_gst_set_int(appsink, maxBuffers, C.gint(2))
+	} else {
+		C.vt_gst_set_int(appsink, maxBuffers, C.gint(1))
+	}
 	C.free(unsafe.Pointer(maxBuffers))
 	dropName := C.CString("drop")
-	C.vt_gst_set_bool(appsink, dropName, C.gboolean(1))
+	if p.preview {
+		C.vt_gst_set_bool(appsink, dropName, C.gboolean(1))
+	} else {
+		C.vt_gst_set_bool(appsink, dropName, C.gboolean(0))
+	}
 	C.free(unsafe.Pointer(dropName))
 
 	var audioSink *C.GstElement
@@ -366,6 +374,7 @@ func (p *GStreamerPlayer) primeAfterSeekLocked() {
 	if p.appsink == nil {
 		return
 	}
+	p.drainPendingLocked()
 	frame, err := p.readFrameLocked(C.GstClockTime(200 * 1000 * 1000))
 	if err != nil || frame == nil {
 		return
@@ -373,6 +382,19 @@ func (p *GStreamerPlayer) primeAfterSeekLocked() {
 	p.queued = frame
 }
 
+func (p *GStreamerPlayer) drainPendingLocked() {
+	if p.appsink == nil {
+		return
+	}
+	for i := 0; i < 5; i++ {
+		sample := C.gst_app_sink_try_pull_sample((*C.GstAppSink)(unsafe.Pointer(p.appsink)), C.GstClockTime(0))
+		if sample == nil {
+			return
+		}
+		C.gst_sample_unref(sample)
+	}
+}
+
 func (p *GStreamerPlayer) SetVolume(level float64) error {
 	p.mu.Lock()
 	defer p.mu.Unlock()

main.go

@@ -11437,9 +11437,12 @@ func (p *playSession) frameDisplayLoop() {
 
 			// Get current time from GStreamer
 			currentTime := p.gstPlayer.GetCurrentTime()
+			p.mu.Lock()
+			isPaused := p.paused
+			p.mu.Unlock()
 
 			// Skip if this is the same frame as last time (optimization)
-			if currentTime == lastFrameTime && frameCount > 0 {
+			if currentTime == lastFrameTime && frameCount > 0 && !isPaused {
 				continue
 			}
 			lastFrameTime = currentTime
@@ -11452,7 +11455,6 @@ func (p *playSession) frameDisplayLoop() {
 			p.mu.Lock()
 			p.frameN = actualFrameNumber
 			p.current = currentTime.Seconds()
-			isPaused := p.paused
 			p.mu.Unlock()
 
 			// Update UI on main thread