hlsdemux2: Resync stream time on partial segment boundaries

When resyncing stream times in a playlist, support at any partial segment
position, not just at full segment boundaries.

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

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

@@ -1383,23 +1383,41 @@ gst_hlsdemux_handle_internal_time (GstHLSDemux * demux,
       GST_STIME_ARGS (real_stream_time), GST_STIME_ARGS (difference));
 
   if (ABS (difference) > 10 * GST_MSECOND) {
-    /* FIXME: LL-HLS could recalculate stream times on parts.
+    GstClockTimeDiff wrong_position_threshold =
-     * For now, only do it at the first part in a segment */
+        hls_stream->current_segment->duration / 2;
-    if (!hls_stream->in_partial_segments || hls_stream->part_idx == 0) {
-      /* Update the value */
-      GST_DEBUG_OBJECT (hls_stream,
-          "Updating current stream time to %" GST_STIME_FORMAT,
-          GST_STIME_ARGS (real_stream_time));
-      current_segment->stream_time = real_stream_time;
 
+    /* Update the value */
+    GST_DEBUG_OBJECT (hls_stream,
+        "Updating current stream time to %" GST_STIME_FORMAT,
+        GST_STIME_ARGS (real_stream_time));
+
+    /* For LL-HLS, make sure to update and recalculate stream time from
+     * the right partial segment if playing one */
+    if (hls_stream->in_partial_segments && hls_stream->part_idx != 0) {
+      if (current_segment->partial_segments
+          && hls_stream->part_idx < current_segment->partial_segments->len) {
+        GstM3U8PartialSegment *part =
+            g_ptr_array_index (current_segment->partial_segments,
+            hls_stream->part_idx);
+        part->stream_time = real_stream_time;
+
+        gst_hls_media_playlist_recalculate_stream_time_from_part
+            (hls_stream->playlist, hls_stream->current_segment,
+            hls_stream->part_idx);
+
+        /* When playing partial segments, the "Wrong position" threshold should be
+         * half the part duration */
+        wrong_position_threshold = part->duration / 2;
+      }
+    } else {
+      /* Aligned to the start of the segment, update there */
+      current_segment->stream_time = real_stream_time;
       gst_hls_media_playlist_recalculate_stream_time (hls_stream->playlist,
           hls_stream->current_segment);
-      gst_hls_media_playlist_dump (hls_stream->playlist);
     }
+    gst_hls_media_playlist_dump (hls_stream->playlist);
 
-    /* FIXME: When playing partial segments, the threshold should be
+    if (ABS (difference) > wrong_position_threshold) {
-     * half the part duration */
-    if (ABS (difference) > (hls_stream->current_segment->duration / 2)) {
       GstAdaptiveDemux2Stream *stream = (GstAdaptiveDemux2Stream *) hls_stream;
       GstM3U8SeekResult seek_result;
 

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

@@ -1667,6 +1667,35 @@ gst_hls_media_playlist_recalculate_stream_time (GstHLSMediaPlaylist * playlist,
   }
 }
 
+void
+gst_hls_media_playlist_recalculate_stream_time_from_part (GstHLSMediaPlaylist *
+    playlist, GstM3U8MediaSegment * anchor, guint part_idx)
+{
+  g_assert (anchor->partial_segments != NULL
+      && part_idx < anchor->partial_segments->len);
+
+  GstClockTimeDiff last_stream_time;
+  GstM3U8PartialSegment *part =
+      g_ptr_array_index (anchor->partial_segments, part_idx);
+  GstM3U8PartialSegment *cand, *prev;
+  gint iter;
+
+  /* Work backward from the target partial segment, assigning stream times until
+   * we update the segment time itself, then recalculate all stream times */
+  prev = part;
+  last_stream_time = part->stream_time;
+  for (iter = part_idx - 1; iter >= 0; iter--) {
+    cand = g_ptr_array_index (anchor->partial_segments, iter);
+    last_stream_time = cand->stream_time = prev->stream_time - cand->duration;
+    GST_DEBUG ("Backward partial segment iter %d %" GST_STIME_FORMAT, iter,
+        GST_STIME_ARGS (cand->stream_time));
+    prev = cand;
+  }
+  anchor->stream_time = last_stream_time;
+
+  gst_hls_media_playlist_recalculate_stream_time (playlist, anchor);
+}
+
 /* If a segment with the same URI, size, offset, SN and DSN is present in the
  * playlist, returns that one */
 static GstM3U8MediaSegment *

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

@@ -279,6 +279,10 @@ void
 gst_hls_media_playlist_recalculate_stream_time (GstHLSMediaPlaylist *playlist,
 						GstM3U8MediaSegment *anchor);
 
+void
+gst_hls_media_playlist_recalculate_stream_time_from_part (GstHLSMediaPlaylist *playlist,
+						GstM3U8MediaSegment *anchor, guint part_idx);
+
 GstM3U8MediaSegment *
 gst_hls_media_playlist_sync_to_segment      (GstHLSMediaPlaylist * m3u8,
 					     GstM3U8MediaSegment * segment);