[rygel] engine-gst: Make it possible to override preroll

[Jens Georg <jensgeorg src gnome org>]

commit 1ad798e31db4ebd17a58dad264c5a595a02057ab
Author: Jens Georg <mail jensge org>
Date:   Sat May 2 12:52:52 2020 +0200

    engine-gst: Make it possible to override preroll

 src/media-engines/gstreamer/rygel-gst-data-source.vala             | 2 +-
 src/media-engines/gstreamer/rygel-gst-transcoding-data-source.vala | 7 +++++++
 2 files changed, 8 insertions(+), 1 deletion(-)
---
diff --git a/src/media-engines/gstreamer/rygel-gst-data-source.vala 
b/src/media-engines/gstreamer/rygel-gst-data-source.vala
index e2ac9ba7..b16562d2 100644
--- a/src/media-engines/gstreamer/rygel-gst-data-source.vala
+++ b/src/media-engines/gstreamer/rygel-gst-data-source.vala
@@ -65,7 +65,7 @@ internal class Rygel.GstDataSource : Rygel.DataSource, GLib.Object {
         return this.seek;
     }
 
-    public Gee.List<HTTPResponseElement>? preroll
+    public virtual Gee.List<HTTPResponseElement>? preroll
                                         (HTTPSeekRequest? seek_request,
                                          PlaySpeedRequest? playspeed_request)
                                          throws Error {
diff --git a/src/media-engines/gstreamer/rygel-gst-transcoding-data-source.vala 
b/src/media-engines/gstreamer/rygel-gst-transcoding-data-source.vala
index 16f2e77e..6df45afa 100644
--- a/src/media-engines/gstreamer/rygel-gst-transcoding-data-source.vala
+++ b/src/media-engines/gstreamer/rygel-gst-transcoding-data-source.vala
@@ -48,6 +48,13 @@ internal class Rygel.TranscodingGstDataSource : Rygel.GstDataSource {
         bin.add_pad (ghost);
     }
 
+    public override Gee.List<HTTPResponseElement>? preroll
+                                        (HTTPSeekRequest? seek_request,
+                                         PlaySpeedRequest? playspeed_request)
+                                         throws Error {
+        return base.preroll (seek_request, playspeed_request);
+    }
+
     private Gst.Pad? get_compatible_sink_pad (Pad pad, Caps caps) {
         var sinkpad = this.encoder.get_compatible_pad (pad, null);