adaptivedemux2: Handle early key-unit seek

Is a seek is done on stream-collection post, there are no selected streams
yet. Therefore none would be chosen to adjust the key-unit seek.

If no streams are selected, fallback to a default stream (i.e. one which has
track(s) with GST_STREAM_FLAG_SELECT).

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/3914>

subprojects/gst-plugins-good/ext/adaptivedemux2/gstadaptivedemux-private.h

@@ -199,6 +199,7 @@ gboolean gst_adaptive_demux_get_live_seek_range (GstAdaptiveDemux * demux,
 gboolean gst_adaptive_demux2_stream_in_live_seek_range (GstAdaptiveDemux * demux,
     GstAdaptiveDemux2Stream * stream);
 gboolean gst_adaptive_demux2_stream_is_selected_locked (GstAdaptiveDemux2Stream *stream);
+gboolean gst_adaptive_demux2_stream_is_default_locked (GstAdaptiveDemux2Stream *stream);
 
 gboolean gst_adaptive_demux_has_next_period (GstAdaptiveDemux * demux);
 void gst_adaptive_demux_advance_period (GstAdaptiveDemux * demux);

subprojects/gst-plugins-good/ext/adaptivedemux2/gstadaptivedemux-stream.c

@@ -2229,6 +2229,20 @@ gst_adaptive_demux2_stream_is_selected_locked (GstAdaptiveDemux2Stream * stream)
   return FALSE;
 }
 
+gboolean
+gst_adaptive_demux2_stream_is_default_locked (GstAdaptiveDemux2Stream * stream)
+{
+  GList *tmp;
+
+  for (tmp = stream->tracks; tmp; tmp = tmp->next) {
+    GstAdaptiveDemuxTrack *track = tmp->data;
+    if (track->flags & GST_STREAM_FLAG_SELECT)
+      return TRUE;
+  }
+
+  return FALSE;
+}
+
 /**
  * gst_adaptive_demux2_stream_is_selected:
  * @stream: A #GstAdaptiveDemux2Stream

subprojects/gst-plugins-good/ext/adaptivedemux2/gstadaptivedemux.c

@@ -2267,9 +2267,14 @@ gst_adaptive_demux_handle_seek_event (GstAdaptiveDemux * demux,
 
   GST_ADAPTIVE_DEMUX_SEGMENT_LOCK (demux);
 
+  if (IS_SNAP_SEEK (flags)) {
+    GstAdaptiveDemux2Stream *default_stream = NULL;
+    GstAdaptiveDemux2Stream *stream = NULL;
+    GList *iter;
     /*
      * Handle snap seeks as follows:
      * 1) do the snap seeking a (random) active stream
+     * 1.1) If none are active yet (early-seek), pick a random default one
      * 2) use the final position on this stream to seek
      *    on the other streams to the same position
      *
@@ -2278,8 +2283,6 @@ gst_adaptive_demux_handle_seek_event (GstAdaptiveDemux * demux,
      * position.
      */
 
-  GstAdaptiveDemux2Stream *stream = NULL;
-  GList *iter;
     /* Pick a random active stream on which to do the stream seek */
     for (iter = demux->output_period->streams; iter; iter = iter->next) {
       GstAdaptiveDemux2Stream *cand = iter->data;
@@ -2287,9 +2290,15 @@ gst_adaptive_demux_handle_seek_event (GstAdaptiveDemux * demux,
         stream = cand;
         break;
       }
+      if (default_stream == NULL
+          && gst_adaptive_demux2_stream_is_default_locked (cand))
+        default_stream = cand;
     }
 
-  if (stream && IS_SNAP_SEEK (flags)) {
+    if (stream == NULL)
+      stream = default_stream;
+
+    if (stream) {
       GstClockTimeDiff ts;
       GstSeekFlags stream_seek_flags = flags;
 
@@ -2332,11 +2341,14 @@ gst_adaptive_demux_handle_seek_event (GstAdaptiveDemux * demux,
         GST_ADAPTIVE_SCHEDULER_UNLOCK (demux);
         GST_ADAPTIVE_DEMUX_SEGMENT_UNLOCK (demux);
 
-      GST_API_UNLOCK (demux);
-      gst_event_unref (event);
-      return FALSE;
-    }
 
+        GST_API_UNLOCK (demux);
+
+        gst_event_unref (event);
+
+        return FALSE;
+
+      }
       /* replace event with a new one without snapping to seek on all streams */
       gst_event_unref (event);
       if (rate >= 0) {
@@ -2349,6 +2361,7 @@ gst_adaptive_demux_handle_seek_event (GstAdaptiveDemux * demux,
           start_type, start, stop_type, stop);
       GST_DEBUG_OBJECT (demux, "Adapted snap seek to %" GST_PTR_FORMAT, event);
     }
+  }
 
   ret = gst_segment_do_seek (&demux->segment, rate, format, flags, start_type,
       start, stop_type, stop, &update);