matroskamux: write subtitle codec ID and data at start when known

This avoids issues with writing dummy data first, then having
to come back and write correct data later. Doing so prevents
the muxed stream from being actually streamable.

https://bugzilla.gnome.org/show_bug.cgi?id=712134

diff --git a/gst/matroska/matroska-mux.c b/gst/matroska/matroska-mux.c
index b79edb1..e594fbc 100644 (file)
--- a/gst/matroska/matroska-mux.c
+++ b/gst/matroska/matroska-mux.c
@@ -2378,7 +2378,13 @@ gst_matroska_mux_track_header (GstMatroskaMux * mux,
     case GST_MATROSKA_TRACK_TYPE_SUBTITLE:{
       gpointer buf;
 
+      /* If codec_id and codec data are already known, we can write
+         them now, as for audio/video */
+      if (context->codec_id && context->codec_priv)
+        break;
+
       context->pos = ebml->pos;
+
       /* CodecID is mandatory ... */
       gst_ebml_write_ascii (ebml, GST_MATROSKA_ID_CODECID, "S_SUB_UNKNOWN");
       /* reserve space */