[gst-devel] write ogg tags

[René Stadler]

Am Dienstag, den 02.01.2007, 18:08 +0100 schrieb Andreas Volz:
> Am Mon, 01 Jan 2007 23:52:43 +0000 schrieb Tim Müller:
> 
> > On Mon, 2007-01-01 at 22:14 +0100, Andreas Volz wrote:
> > 
> > > Yes, this really helps. I write the tags only while encoding. Do you
> > > know a player that shows really *all* Vorbis tags? Most player show
> > > only some tags. But I need to display some uncommon tags like e.g.
> > > location. Is my only choose to write my own little player?
> > 
> > Not sure I understand what you're really after, but
> > 
> >   gst-launch-0.10 -t playbin uri=file:///home/andreas/foo.ogg
> > 
> > should show _all_ vorbis tags in one way or another (at least with the
> > latest released gstreamer + gst-plugins-base versions). Tags for which
> > there are no explicit GStreamer tags should then show up as
> > GST_TAG_EXTENDED_COMMENT (which is basically a key=value string tag).
> > There's a utility function in libgsttag (part of the gst-plugins-base
> > libs) to parse those as well.
> 
> Yes, this is good enough. I don't need a complete player. It was only
> to control that all tags are correct written. But not all tags are
> printed. GST_TAG_LOCATION wasn't printed by the above command. See here
> the source:
> 
>   gst_tag_setter_add_tags (tagsetter,
>                            GST_TAG_MERGE_REPLACE_ALL,
>                            GST_TAG_TITLE, "Geo Tagged Voice",
> 			   GST_TAG_ARTIST, "GPSTrigger",
> 			   GST_TAG_LOCATION, "GPS 123456790",
> 			   GST_TAG_VERSION, "0.1",
> 			   GST_TAG_LICENSE, "Creative Commons
> 				Attribution-ShareAlike 2.5", NULL);

Try changing GST_TAG_LOCATION to GST_TAG_EXTENDED_COMMENT and "GPS
123456790" to "location=GPS 123456790" (see below).

> result:
> > gst-launch-0.10 -t playbin uri=file://sound.ogg
> Setting pipeline to PAUSED ...
> Pipeline is PREROLLING ...
> KENNZEICHEN GEFUNDEN: Von Element »vorbisdec1« gefunden.
>            Titel: Geo Tagged Voice
>        Künstler: GPSTrigger
>          Version: 0.1
>           Lizenz: Creative Commons Attribution-ShareAlike 2.5
>         Codierer: Xiph.Org libVorbis I 20050304
> Version des Codierers: 0
>      Audio-Codec: Vorbis
>  Normale Bitrate: 80000
>          Bitrate: 80000
> Pipeline is PREROLLED ...
> Setting pipeline to PLAYING ...
> New clock: audioclock1
> Got EOS from element "playbin0".
> Execution ended after 1322854000 ns.
> Setting pipeline to PAUSED ...
> Setting pipeline to READY ...
> Setting pipeline to NULL ...
> FREEING pipeline ...
> 
> So there's GST_TAG_LOCATION. Where is it?
> 
> BTW: I need this to tag voices with geographic information.

A quick peek at gst-plugins-base/gst-libs/gst/tag/gstvorbistag.c shows
that GST_TAG_LOCATION is not supported.  Does the vorbis spec dictate
how geo locations are to be stored?  Are there programs that do it?  If
not, what you try to do is a non-standard extension.  You need to store
your data with GST_TAG_EXTENDED_COMMENT in this case, which works nicely
since vorbis allows for arbitrary key=value pairs.

The real problem is that since vorbisenc does not know how to store
GST_TAG_LOCATION tags, it silently discards them.  This is how all gst
tag writers handle unknown meta data, and it sucks because there is no
way to detect what a tag setter supports and what not.  I opened a bug
about that a while ago, you can add yourself to CC there to be notified
when there is any progress in that direction:
http://bugzilla.gnome.org/show_bug.cgi?id=345352

> Another question:
> 
> All string fields are gchar. But what's about other languages like
> chinese or cyrillic? I assume this field is unicode. But UTF8? UTF16?
> Little Endian? Big Endian? I know the situation for MP3 because I read
> the spec some time ago. But how is it for vorbis?

It should be UTF-8, by default glib convention.

> regards
> Andreas

-- 
Regards,
  René Stadler