[ogg-dev] Album art - requirements

[Silvia Pfeiffer]

On Fri, Oct 17, 2008 at 8:51 PM, ogg.k.ogg.k at googlemail.com
<ogg.k.ogg.k at googlemail.com> wrote:
> Hi,
>
> [ Was away the last few days, so this partly overlaps on things that
> that have been mentioned in this thread. Since the consensus seems
> that Vorbis comment encoding is the way to go, it's a bit moot, but
> here it is anyway ]
>
> Following up on the possibility to tag various images as different
> types of album art, I thought of adding that tagging information in
> a Skeleton stream. Since Skeleton's purpose is to describe the set
> of tracks in a physical bitstream, as well as the relationship between
> those tracks, it is well suited to such a use.
>
> So, a possible way to encode album art would be:
>
> - a Skeleton stream with appropriate header messages
> - one Kate stream per image, carrying a PNG image
>  (alternatively, use Ogg/MNG, if someone brings it from the dead)
>
> The semantics of those images would be carried by predefined message
> headers in the Skeleton stream. Something along the lines of (for
> each separate image stream):
>
> X-Content-Semantics: album art
> X-Album-Art-Type: front cover    (or back cover, etc)
>
> There would be some overhead with having one stream per image: Kate
> headers would weight at 162 bytes for header payload, plus two Ogg
> frames at 29 bytes each, and would be per image rather than per file.
> If carrying a 25 KB PNG image, this is only about 0.1% though.
>
> One drawback is streaming, where all of this is stuffed into the
> headers, so there's a biggish hit at connection if sending a stream
> loaded with images. Caveat icecast operator I suppose. Icecast could
> also be made to automatically strip those as an option too, if needed
> (I'd have to look, not sure if this'd be that easy to do).
>
> This is a good chance to actually have Skeleton used for what it's
> meant to be (AFAICT): relationships between tracks: one could define
> a particular image to be related to a particular track, if a whole
> album gets encoded as several Vorbis tracks in a single stream.
> Most of the images would be common to all tracks, but some could
> be track specific. This could also be used for lyrics: map a given
> lyrics track to the matching Vorbis track.
>
> Is there a list of relationships that Skeleton can define somewhere,
> or is this not done yet ?

Interesting proposal. Not sure it won't over-complicate album art though...

BTW: Skeleton has not been invented in the first instance to define
relationships between tracks. It has been invented to describe the
tracks without having to decode them. But the relationships has always
been an idea for it.

At the last FOMS we started defining ROE for describing tracks and
their relationship with each other. Some of the information in ROE
should indeed go into Skeleton upon encoding. Yet, the relationship
part is really challenging an nobody has touched that yet in much
detail.

If you have any ideas on what types of relationships are necessary and
how to describe them, feel free to send something.

Cheers,
Silvia.