mux: mp4: don't create stss for subs

(cherry picked from commit 7d7149c5a61c99aa86f0bc2717a485d6942d8fff)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/mux/mp4.c

@@ -1497,7 +1497,10 @@ static bo_t *GetStblBox(sout_mux_t *p_mux, mp4_stream_t *p_stream)
     /* create stss table */
     bo_t *stss = NULL;
     i_index = 0;
+    if ( p_stream->fmt.i_cat == VIDEO_ES || p_stream->fmt.i_cat == AUDIO_ES )
+    {
         for (unsigned i = 0; i < p_stream->i_entry_count; i++)
+        {
             if (p_stream->entry[i].i_flags & BLOCK_FLAG_TYPE_I) {
                 if (stss == NULL) {
                     stss = box_full_new("stss", 0, 0);
@@ -1506,6 +1509,8 @@ static bo_t *GetStblBox(sout_mux_t *p_mux, mp4_stream_t *p_stream)
                 bo_add_32be(stss, 1 + i);
                 i_index++;
             }
+        }
+    }
 
     if (stss)
         bo_fix_32be(stss, 12, i_index);