qtmux: move subtitle layer above video and set alternate group

layer -1 is above video, that is 0
And having all subtitles in alternate group 2 means that only one
should be selected at a time.

https://bugzilla.gnome.org/show_bug.cgi?id=737095

diff --git a/gst/isomp4/atoms.c b/gst/isomp4/atoms.c
index f8bf050..b27abc7 100644 (file)
--- a/gst/isomp4/atoms.c
+++ b/gst/isomp4/atoms.c
@@ -3426,6 +3426,9 @@ atom_trak_set_subtitle_commons (AtomTRAK * trak, AtomsContext * context)
 {
   atom_trak_set_subtitle (trak, context);
   trak->mdia.mdhd.time_info.timescale = 1000;
+
+  trak->tkhd.alternate_group = 2;       /* same for all subtitles */
+  trak->tkhd.layer = -1;        /* above video (layer 0) */
 }
 
 void