hls/m3u8: Fix starting segment for live playlist

RFC 8216 6.3.3 "Playing the Media Playlist File" : states that for live media
playlists "the client SHOULD NOT choose a segment that starts less than three
target durations from the end of the Playlist file"

This is an off-by-one error. Since we are looking for the "index" of the
segment, we need to subtract 1 from the searched position.

Ex: For a playlist with 12 entries, we want to start playback on the 9th segment
... which is at index 8.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/2259>

diff --git a/subprojects/gst-plugins-good/ext/adaptivedemux2/hls/m3u8.c b/subprojects/gst-plugins-good/ext/adaptivedemux2/hls/m3u8.c
index f976b2f..0b8bf16 100644 (file)
--- a/subprojects/gst-plugins-good/ext/adaptivedemux2/hls/m3u8.c
+++ b/subprojects/gst-plugins-good/ext/adaptivedemux2/hls/m3u8.c
@@ -1124,8 +1124,8 @@ gst_hls_media_playlist_get_starting_segment (GstHLSMediaPlaylist * self)
     /* Live playlist */
     res =
         g_ptr_array_index (self->segments,
-        MAX ((gint) self->segments->len - GST_M3U8_LIVE_MIN_FRAGMENT_DISTANCE,
-            0));
+        MAX ((gint) self->segments->len - GST_M3U8_LIVE_MIN_FRAGMENT_DISTANCE -
+            1, 0));
   }
 
   if (res) {