[Vorbis-dev] Cover art

[Tor-Einar Jarnbjo]

Ian Malone schrieb:
> Yes it's not ideal, but I'm reasoning on the basis that all the specs
> dealing with the vorbis comment headers (or its clones in other
> formats) require the comment contents to be UTF-8 encoded.  This
> presumably means the picture description is UTF-8 encoded twice.
>   
I was wondering about this myself, as the proposal on 
http://wiki.xiph.org/index.php/VorbisComment didn't mention anything 
about UTF-8 encoding the binary content of the coverart structure, 
although it's done in the demo file. If not doing it, arbitrary binary 
content is most likely not a valid UTF-8 sequence and may cause current 
software to fail.

I'm however not sure if having a leading 0 byte in the "string" solves 
too many incompatibilities with old software and if this approach is 
much better than Base64-encoding the data. If the byte values in the 
image structure are equally distributed (with JPEG they most likely 
are), the UTF-8 encoding will add an overhead of 50%, while the Base64 
encoding adds an overhead of 33%. Even if older software displays the 
Base64 comment value as a string, it's unlikely that the comment is 
ignored completely, as is the case with e.g. WinAmp. Not only is the 
BINARY_COVERART not shown in the file info dialog, but it's removed from 
the file if other comments are edited with WinAmp.

I'm also honestly not 100% sure how C/C++ is handling Unicode strings 
(it was not really a topic the last time I wrote anything in C), but 
0x00 is actually a valid Unicode control character and will not always 
be treated as an end of string marker by current software, so using 
UTF-8 encoding instead of Base64 does not guarantee, that the content is 
not treated as a string and shown:

http://jarnbjo.de/screenshot.png

Tor