hlsdemux2: Improve media playlist updates

* When dealing with rendition streams, we attempt to synchronize the media
  playlist against the variant stream. This helps with speeding up the correct
  initial fragment search and avoids issues when streams at activated at a much
  later time.
* Also add checks for variant stream existence before attempting to use them

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/2679>

1 files changed, 26 insertions, 17 deletions

diff --git a/subprojects/gst-plugins-good/ext/adaptivedemux2/hls/gsthlsdemux.c b/subprojects/gst-plugins-good/ext/adaptivedemux2/hls/gsthlsdemux.c
index 1db3271d34..e191298215 100644
--- a/subprojects/gst-plugins-good/ext/adaptivedemux2/hls/gsthlsdemux.c
+++ b/subprojects/gst-plugins-good/ext/adaptivedemux2/hls/gsthlsdemux.c
@@ -1956,24 +1956,33 @@ gst_hls_demux_stream_update_media_playlist (GstHLSDemux * demux,
   }
 
   /* Synchronize playlist with previous one */
-  if (stream->playlist) {
-    if (!gst_hls_media_playlist_sync_to_playlist (new_playlist,
-            stream->playlist)) {
-      /* Failure to sync is only fatal for variant streams. */
-      if (stream->is_variant) {
-        GST_ERROR_OBJECT (stream,
-            "Could not synchronize new variant playlist with previous one !");
-        return FALSE;
-      }
-      /* For rendition streams, we can attempt synchronization against the
-       * variant playlist which is constantly updated */
-      if (!gst_hls_media_playlist_sync_to_playlist (new_playlist,
-              demux->main_stream->playlist)) {
-        GST_ERROR_OBJECT (stream,
-            "Could not do fallback synchronization of rendition stream to variant stream");
-        return FALSE;
-      }
+  if (stream->playlist
+      && !gst_hls_media_playlist_sync_to_playlist (new_playlist,
+          stream->playlist)) {
+    /* Failure to synchronize with the previous media playlist is only fatal for
+     * variant streams. */
+    if (stream->is_variant) {
+      GST_ERROR_OBJECT (stream,
+          "Could not synchronize new variant playlist with previous one !");
+      return FALSE;
     }
+
+    /* For rendition streams, we can attempt synchronization against the
+     * variant playlist which is constantly updated */
+    if (demux->main_stream->playlist
+        && !gst_hls_media_playlist_sync_to_playlist (new_playlist,
+            demux->main_stream->playlist)) {
+      GST_ERROR_OBJECT (stream,
+          "Could not do fallback synchronization of rendition stream to variant stream");
+      return FALSE;
+    }
+  } else if (!stream->is_variant && demux->main_stream->playlist) {
+    /* For initial rendition media playlist, attempt to synchronize the playlist
+     * against the variant stream. This is non-fatal if it fails. */
+    GST_DEBUG_OBJECT (stream,
+        "Attempting to synchronize initial rendition stream with variant stream");
+    gst_hls_media_playlist_sync_to_playlist (new_playlist,
+        demux->main_stream->playlist);
   }
 
   if (stream->current_segment) {