[ogg-dev] embedded pictures in vorbis comments?

[Ralph Giles]

On Sat, Apr 28, 2007 at 11:09:03AM +0000, Mathias Kunter wrote:

> I think we can start by defining an official field name at www.xiph.org/vorbis/doc/v-comment.html which is used as a file system link to an existing image file. I suggest the field name to be "PICTURE".

That's fine. Note that FLAC imports some other fields, like media-type 
and "picture type", an enumeration of semantic categories, from the 
id3v2 spec for it's picture metadata block.

> What is ogg MNG? Is it a container format for PNG files which should be embedded in OGG files?

MNG is a superset of PNG and JPEG. There's a general proposal for using 
it as the standard for embedding PNG, JPEG, mJPEG, lossless video, 
DVD-style graphical overlays, station-id bugs, etc. in Ogg streams. 

  http://libpng.org/pub/mng/
  http://wiki.xiph.org/OggMNG

OggSpots was a simpler proposal to embed single or sequences of PNG or 
jpeg images without the MNG wrapper.

> If I understand correctly, the picture would be placed in a different logical stream inside the ogg file. The question is how many players or taggers are going to support this. For example, I saw that WinAmp (version 5.32) can't tag multiplexed ogg vorbis files correctly (it ruined a ogg vorbis + theora file so that only the music could be played afterwards, but not the video any more). My .NET tagging library can handle it correctly now by the way ;-)

Yes, the picture would be placed in a separate logical stream, with an 
OggSkeleton header marking its intended use. Nothing supports that yet,
but nothing supports the vorbis-comment extension either, so that's not
really an argument.

More seriously, the Ogg Vorbis spec says that decoders are allowed to 
reject multiplexed streams, so such files may not work with a lot of
current audio software and embedded players. (Video players work fine.)
So while the multiplexed image stream is what we should do, it probably 
makes sense to support a vorbiscomment option as well as the freedesktop 
directory-icon pseudo-standard for albums. :(

 -r