diff --git a/pkg/cmd/whip.go b/pkg/cmd/whip.go
index 2f67e8b66..920f47020 100644
--- a/pkg/cmd/whip.go
+++ b/pkg/cmd/whip.go
@@ -74,8 +74,13 @@ func (w *WHIPClient) WHIP(ctx context.Context) error {
 		"filesrc name=filesrc ! qtdemux name=demux",
 		"demux.video_0 ! tee name=video_tee",
 		"demux.audio_0 ! tee name=audio_tee",
-		"video_tee. ! queue ! h264parse config-interval=-1 ! video/x-h264,stream-format=byte-stream ! appsink name=videoappsink",
-		"audio_tee. ! queue ! opusparse ! appsink name=audioappsink",
+		// sync=true (the default) is load-bearing here, unlike every other
+		// appsink in the tree: these sinks are what pace the file at realtime
+		// so it plays as a live stream — WriteSample pushes to WebRTC
+		// immediately, so without clock sync the whole file would blast
+		// through in one burst.
+		"video_tee. ! queue ! h264parse config-interval=-1 ! video/x-h264,stream-format=byte-stream ! appsink sync=true name=videoappsink",
+		"audio_tee. ! queue ! opusparse ! appsink sync=true name=audioappsink",
 		// "matroskamux name=mux ! fakesink name=fakesink sync=true",
 		// "video_tee. ! mux.video_0",
 		// "audio_tee. ! mux.audio_0",
diff --git a/pkg/media/gstreamer.go b/pkg/media/gstreamer.go
index 140f9460d..f3c1f4d11 100644
--- a/pkg/media/gstreamer.go
+++ b/pkg/media/gstreamer.go
@@ -68,6 +68,7 @@ func SelfTest(ctx context.Context) error {
 
 	sinkele, err := gst.NewElementWithProperties("appsink", map[string]interface{}{
 		"name": "self-test-sink",
+		"sync": false,
 	})
 	if err != nil {
 		return fmt.Errorf("failed to create appsink element: %w", err)
diff --git a/pkg/media/thumbnail.go b/pkg/media/thumbnail.go
index 1dd5a9986..7b2d0a0c6 100644
--- a/pkg/media/thumbnail.go
+++ b/pkg/media/thumbnail.go
@@ -71,7 +71,7 @@ func thumbnailFromMP4(ctx context.Context, flat []byte, w io.Writer, format stri
 	pipeline, err := gst.NewPipelineFromString(strings.Join([]string{
 		"appsrc name=src ! decodebin ! videoconvert ! videoscale ! videorate ! capsfilter caps=video/x-raw,width=[1,1280],height=[1,720],pixel-aspect-ratio=1/1,framerate=1/999999 ! ",
 		encoder,
-		" ! appsink name=appsink",
+		" ! appsink sync=false name=appsink",
 	}, "\n"))
 	if err != nil {
 		return fmt.Errorf("create thumbnail pipeline: %w", err)