hlsdemux2: Prune time maps when possible

Add a new method to prune unused time mappings (i.e. which aren't used by any
current media playlist).

Do that when doing flushing seeks. Could be used in other places later too.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/2839>

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

@@ -113,6 +113,8 @@ static void
 gst_hls_update_time_mappings (GstHLSDemux * demux,
     GstHLSMediaPlaylist * playlist);
 
+static void gst_hls_prune_time_mappings (GstHLSDemux * demux);
+
 static gboolean gst_hls_demux_seek (GstAdaptiveDemux * demux, GstEvent * seek);
 static GstFlowReturn gst_hls_demux_stream_seek (GstAdaptiveDemux2Stream *
     stream, gboolean forward, GstSeekFlags flags, GstClockTimeDiff ts,
@@ -443,6 +445,7 @@ gst_hls_demux_seek (GstAdaptiveDemux * demux, GstEvent * seek)
   /* properly cleanup pending decryption status */
   if (flags & GST_SEEK_FLAG_FLUSH) {
     gst_hls_demux_clear_all_pending_data (hlsdemux);
+    gst_hls_prune_time_mappings (hlsdemux);
   }
 
   for (walk = demux->input_period->streams; walk; walk = g_list_next (walk)) {
@@ -1190,15 +1193,14 @@ gst_hls_demux_typefind_stream (GstHLSDemux * hlsdemux,
   return TRUE;
 }
 
-GstHLSTimeMap *
+static GstHLSTimeMap *
-gst_hls_find_time_map (GstHLSDemux * demux, gint64 dsn)
+time_map_in_list (GList * list, gint64 dsn)
 {
-  GList *tmp;
+  GList *iter;
 
-  GST_LOG_OBJECT (demux, "dsn:%" G_GINT64_FORMAT, dsn);
+  for (iter = list; iter; iter = iter->next) {
+    GstHLSTimeMap *map = iter->data;
 
-  for (tmp = demux->mappings; tmp; tmp = tmp->next) {
-    GstHLSTimeMap *map = tmp->data;
     if (map->dsn == dsn)
       return map;
   }
@@ -1206,6 +1208,12 @@ gst_hls_find_time_map (GstHLSDemux * demux, gint64 dsn)
   return NULL;
 }
 
+GstHLSTimeMap *
+gst_hls_find_time_map (GstHLSDemux * demux, gint64 dsn)
+{
+  return time_map_in_list (demux->mappings, dsn);
+}
+
 /* Compute the stream time for the given internal time, based on the provided
  * time map.
  *
@@ -1916,7 +1924,49 @@ gst_hls_demux_add_time_mapping (GstHLSDemux * demux, gint64 dsn,
   demux->mappings = g_list_append (demux->mappings, map);
 }
 
-/* Got over the DSN from the playlist and add any missing time mapping */
+/* Remove any time mapping which isn't currently used by any stream playlist */
+static void
+gst_hls_prune_time_mappings (GstHLSDemux * hlsdemux)
+{
+  GstAdaptiveDemux *demux = (GstAdaptiveDemux *) hlsdemux;
+  GList *active = NULL;
+  GList *iterstream;
+
+  for (iterstream = demux->input_period->streams; iterstream;
+      iterstream = iterstream->next) {
+    GstAdaptiveDemux2Stream *stream = iterstream->data;
+    GstHLSDemuxStream *hls_stream = (GstHLSDemuxStream *) stream;
+    gint64 dsn = G_MAXINT64;
+    guint idx, len;
+
+    if (!hls_stream->playlist)
+      continue;
+    len = hls_stream->playlist->segments->len;
+    for (idx = 0; idx < len; idx++) {
+      GstM3U8MediaSegment *segment =
+          g_ptr_array_index (hls_stream->playlist->segments, idx);
+
+      if (dsn == G_MAXINT64 || segment->discont_sequence != dsn) {
+        dsn = segment->discont_sequence;
+        if (!time_map_in_list (active, dsn)) {
+          GstHLSTimeMap *map = gst_hls_find_time_map (hlsdemux, dsn);
+          if (map) {
+            GST_DEBUG_OBJECT (demux,
+                "Keeping active time map dsn:%" G_GINT64_FORMAT, map->dsn);
+            /* Move active dsn to active list */
+            hlsdemux->mappings = g_list_remove (hlsdemux->mappings, map);
+            active = g_list_append (active, map);
+          }
+        }
+      }
+    }
+  }
+
+  g_list_free_full (hlsdemux->mappings, g_free);
+  hlsdemux->mappings = active;
+}
+
+/* Go over the DSN from the playlist and add any missing time mapping */
 static void
 gst_hls_update_time_mappings (GstHLSDemux * demux,
     GstHLSMediaPlaylist * playlist)