hlsdemuxdemux2: Consider the hold-back when calculating seek range

When calculating the seek range for a live stream, use the same hold-back logic
as when choosing a starting segment, including low-latency segments if
enabled. Permits seeking closer to the live edge when re-synching or catching
up.

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

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

@@ -1268,10 +1268,11 @@ gst_hls_demux_get_live_seek_range (GstAdaptiveDemux * demux, gint64 * start,
   GstHLSDemux *hlsdemux = GST_HLS_DEMUX_CAST (demux);
   gboolean ret = FALSE;
 
-  if (hlsdemux->main_stream && hlsdemux->main_stream->playlist)
+  if (hlsdemux->main_stream && hlsdemux->main_stream->playlist) {
     ret =
         gst_hls_media_playlist_get_seek_range (hlsdemux->main_stream->playlist,
-        start, stop);
+        hlsdemux->main_stream->llhls_enabled, start, stop);
+  }
 
   return ret;
 }

subprojects/gst-plugins-good/ext/adaptivedemux2/hls/m3u8.c

@@ -2487,10 +2487,9 @@ gst_hls_media_playlist_has_lost_sync (GstHLSMediaPlaylist * m3u8,
 
 gboolean
 gst_hls_media_playlist_get_seek_range (GstHLSMediaPlaylist * m3u8,
-    gint64 * start, gint64 * stop)
+    gboolean low_latency, gint64 * start, gint64 * stop)
 {
   GstM3U8MediaSegment *first, *last;
-  guint min_distance = 1;
 
   g_return_val_if_fail (m3u8 != NULL, FALSE);
 
@@ -2500,17 +2499,31 @@ gst_hls_media_playlist_get_seek_range (GstHLSMediaPlaylist * m3u8,
   first = g_ptr_array_index (m3u8->segments, 0);
   *start = first->stream_time;
 
-  if (GST_HLS_MEDIA_PLAYLIST_IS_LIVE (m3u8) && m3u8->segments->len > 1) {
+  /* Default is the end of the playlist */
-    /* min_distance is used to make sure the seek range is never closer than
+  last = g_ptr_array_index (m3u8->segments, m3u8->segments->len - 1);
-       GST_M3U8_LIVE_MIN_FRAGMENT_DISTANCE fragments from the end of a live
-       playlist - see 6.3.3. "Playing the Playlist file" of the HLS draft */
-    min_distance =
-        MIN (GST_M3U8_LIVE_MIN_FRAGMENT_DISTANCE, m3u8->segments->len - 1);
-  }
-
-  last = g_ptr_array_index (m3u8->segments, m3u8->segments->len - min_distance);
   *stop = last->stream_time + last->duration;
 
+  /* For live playlists, take the minimum hold back into account
+   * for the end of the seek range */
+  if (GST_HLS_MEDIA_PLAYLIST_IS_LIVE (m3u8)) {
+    GstM3U8SeekResult seek_result;
+
+    if (gst_hls_media_playlist_get_starting_segment (m3u8, low_latency,
+            &seek_result)) {
+      if (seek_result.found_partial_segment) {
+        GstM3U8PartialSegment *part =
+            g_ptr_array_index (seek_result.segment->partial_segments,
+            seek_result.part_idx);
+        *stop = part->stream_time + part->duration;
+      } else {
+        *stop =
+            seek_result.segment->stream_time + seek_result.segment->duration;
+      }
+
+      gst_m3u8_media_segment_unref (seek_result.segment);
+    }
+  }
+
   return TRUE;
 }
 

subprojects/gst-plugins-good/ext/adaptivedemux2/hls/m3u8.h

@@ -335,7 +335,7 @@ gboolean
 gst_hls_media_playlist_is_live              (GstHLSMediaPlaylist * m3u8);
 
 gboolean
-gst_hls_media_playlist_get_seek_range       (GstHLSMediaPlaylist * m3u8,
+gst_hls_media_playlist_get_seek_range       (GstHLSMediaPlaylist * m3u8, gboolean low_latency,
 					     gint64  * start,
 					     gint64  * stop);
 

subprojects/gst-plugins-good/tests/check/elements/hlsdemux_m3u8.c

@@ -524,7 +524,8 @@ GST_START_TEST (test_playlist_with_doubles_duration)
   assert_equals_float (file->duration / (double) GST_SECOND, 10.2344);
   file = GST_M3U8_MEDIA_SEGMENT (g_ptr_array_index (pl->segments, 3));
   assert_equals_float (file->duration / (double) GST_SECOND, 9.92);
-  fail_unless (gst_hls_media_playlist_get_seek_range (pl, &start, &stop));
+  fail_unless (gst_hls_media_playlist_get_seek_range (pl, FALSE, &start,
+          &stop));
   assert_equals_int64 (start, 0);
   assert_equals_float (stop / (double) GST_SECOND,
       10.321 + 9.6789 + 10.2344 + 9.92);