hlsdemux2: Use partial segment for playlist update interval

When playing LL-HLS playlists in LL-HLS mode, update the playlist more often (on
the partial segment interval) or else we end up downloading them in bursts and
playing further from the live edge than intended.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/3883>

subprojects/gst-plugins-good/ext/adaptivedemux2/hls/gsthlsdemux-stream.c

@@ -1675,6 +1675,58 @@ lost_sync:
   }
 }
 
+GstClockTime
+gst_hls_demux_stream_get_playlist_reload_interval (GstHLSDemuxStream * stream)
+{
+  GstHLSMediaPlaylist *playlist = stream->playlist;
+
+  if (playlist == NULL)
+    return GST_CLOCK_TIME_NONE; /* No playlist yet */
+
+  if (!gst_hls_media_playlist_is_live (playlist))
+    return GST_CLOCK_TIME_NONE; /* Not live playback */
+
+  /* Use the most recent segment (or part segment) duration, as per
+   * https://datatracker.ietf.org/doc/html/draft-pantos-hls-rfc8216bis-11#section-6.3.4
+   */
+  GstClockTime target_duration = GST_CLOCK_TIME_NONE;
+  GstClockTime min_reload_interval = playlist->targetduration / 2;
+
+  if (playlist->segments->len) {
+    GstM3U8MediaSegment *last_seg =
+        g_ptr_array_index (playlist->segments, playlist->segments->len - 1);
+
+    target_duration = last_seg->duration;
+
+    if (stream->llhls_enabled && last_seg->partial_segments) {
+      GstM3U8PartialSegment *last_part =
+          g_ptr_array_index (last_seg->partial_segments,
+          last_seg->partial_segments->len - 1);
+
+      target_duration = last_part->duration;
+      if (GST_CLOCK_TIME_IS_VALID (playlist->partial_targetduration)) {
+        min_reload_interval = playlist->partial_targetduration / 2;
+      } else {
+        min_reload_interval = target_duration / 2;
+      }
+    }
+  } else if (stream->llhls_enabled
+      && GST_CLOCK_TIME_IS_VALID (playlist->partial_targetduration)) {
+    target_duration = playlist->partial_targetduration;
+    min_reload_interval = target_duration / 2;
+  } else if (playlist->version > 5) {
+    target_duration = playlist->targetduration;
+  }
+
+  if (playlist->reloaded && target_duration > min_reload_interval) {
+    GST_DEBUG_OBJECT (stream,
+        "Playlist didn't change previously, returning lower update interval");
+    target_duration = min_reload_interval;
+  }
+
+  return target_duration;
+}
+
 static GstFlowReturn
 gst_hls_demux_stream_update_rendition_playlist (GstHLSDemux * demux,
     GstHLSDemuxStream * stream)

subprojects/gst-plugins-good/ext/adaptivedemux2/hls/gsthlsdemux-stream.h

@@ -165,6 +165,9 @@ gst_hls_demux_stream_seek (GstAdaptiveDemux2Stream * stream, gboolean forward,
 GstFlowReturn
 gst_hls_demux_stream_update_media_playlist (GstHLSDemuxStream * stream, gchar ** uri, GError ** err);
 
+GstClockTime
+gst_hls_demux_stream_get_playlist_reload_interval (GstHLSDemuxStream * stream);
+
 void
 gst_hls_demux_stream_clear_pending_data (GstHLSDemuxStream * hls_stream,
     gboolean force);

subprojects/gst-plugins-good/ext/adaptivedemux2/hls/gsthlsdemux.c

@@ -745,7 +745,7 @@ gst_hls_demux_is_live (GstAdaptiveDemux * demux)
   GstHLSDemux *hlsdemux = GST_HLS_DEMUX_CAST (demux);
   gboolean is_live = FALSE;
 
-  if (hlsdemux->main_stream)
+  if (hlsdemux->main_stream && hlsdemux->main_stream->playlist)
     is_live = gst_hls_media_playlist_is_live (hlsdemux->main_stream->playlist);
 
   return is_live;
@@ -1258,22 +1258,11 @@ gst_hls_demux_get_manifest_update_interval (GstAdaptiveDemux * demux)
 {
   GstHLSDemux *hlsdemux = GST_HLS_DEMUX_CAST (demux);
   GstClockTime target_duration = 5 * GST_SECOND;
+  GstHLSDemuxStream *main_stream = hlsdemux->main_stream;
 
-  if (hlsdemux->main_stream && hlsdemux->main_stream->playlist) {
+  if (main_stream) {
-    GstHLSMediaPlaylist *playlist = hlsdemux->main_stream->playlist;
+    target_duration =
-
+        gst_hls_demux_stream_get_playlist_reload_interval (main_stream);
-    if (playlist->version > 5) {
-      target_duration = hlsdemux->main_stream->playlist->targetduration;
-    } else if (playlist->segments->len) {
-      GstM3U8MediaSegment *last_seg =
-          g_ptr_array_index (playlist->segments, playlist->segments->len - 1);
-      target_duration = last_seg->duration;
-    }
-    if (playlist->reloaded && target_duration > (playlist->targetduration / 2)) {
-      GST_DEBUG_OBJECT (demux,
-          "Playlist didn't change previously, returning lower update interval");
-      target_duration /= 2;
-    }
   }
 
   GST_DEBUG_OBJECT (demux, "Returning update interval of %" GST_TIME_FORMAT,