Thursday, July 29. 2004

A bright coloured fish

Screenshot: evidence file-manager with fish theme
Modern formats like Ogg Vorbis or MP3 do not only allow you to store you music in compressed form, they also facilitate "tagging" it, i.e., storing meta-data like the artist, the album the song is on and the year when it was released in a portion of the file called the "tag." The standard that describes tags for MP3 files is called ID3, and few people know that ID3 tags may contain images of the artist, the album's cover, or a variety of other things. (Of course, the evidence file-manager supports ID3 and will display an image from the tag instead of the generic "MP3-song" icon if one is found.)
The common response to this gem is people calling such tags bloat.
The common response to that is that 10 KB of JPG image in 6 MB of MP3 doesn't exactly constitute bloat.
Sometimes, this answer is spiced up with a little calculation illustrating how many image tags you'd have to create before stealing diskspace for even one soundfile.
The list of supported image-IDs is rather comprehensive: Other, icon (32x32 PNG), file icon, Cover (front), Cover (back), Leaflet page, Media, Lead artist/lead performer/soloist, Artist/performer, Conductor, Band/Orchestra, Composer, Lyricist/text writer, Recording Location, During recording, During performance, Movie/video screen capture, a bright coloured fish, Illustration, Band/artist logotype, and finally Publisher/Studio logotype.
So, if you ever come across the fishie in the wild, let me know! (Thanks in advance for all the fish!)
Posted by Azundris in English at 14:38 | Comments (7) | Trackbacks (0)
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Lewe on :

*I've always asked myself where you hid all the time, and now that Kris visited me I saw what beautiful piece of software you created. I can't wait for the new enlightenment and I am anxious to try out that file manager of yours. I don't use file managers too much 'till today but yours souds very promising. Keep it up! :)

Azundris on :

*Thank you for your kind words about evidence.
I think part of what makes it interesting is that it is a file-manager for shell-users, by shell-users.
I've never used nautilus or konqueror for a variety of reasons, and at first I wasn't convinced I'd actually use evidence. Nowadays, I do about 5o % of my file-managing in evidence and 5o % in the shell. Basically whenever previews come in handy, evidence wins hands down. Imagine looking for a particular image in a hundred that you downloaded from your digitical camera. Ultra-fast JPEG thumbnailing, support for EXIF, ID3/Ogg tag editing, actions for renaming the file from the tag (or tagging based on the file-name) etc. make ev really useful when working with media.

bronius on :

*Is it correct to say, then, that ID3 indeed embeds actual image data into the mp3 and not just a URI of some sort?

Azundris on :

*This usually correct. : )

Normally, an image of a well-known type (JPEG, PNG, ...) will be embedded. It is however also possible to embed an URL instead of the actual image data.

While this may seem silly at first (given that usually the image isn't all that big compared to the actual sound data, especially when the former is JPEG-compressed), it can be argued that if you actually want to include decent-quality images of all of the types (composer, cover, ...), and you have an album full of songs for which most of these images don't change (for instance, the album-cover is the same for each song), avoiding the redudancy may be desirable.

As stated above, several images may pertain to each song-file. The MIME-type for each image is explicitly noted; each image may therefore be of a different MIME-type. (This would imply that some you can mix in-band per-song images and out-of-band per-album or per-band images.) If the MIME-type (denoting embedded image data) is missing in favour of the magic marker "-->", an out-of-band image referenced by an URL (as per RfC 1738) is assumed. This seems interesting specifically for absolute HTTP-URLs and relative URLs (using the URL of the MP3 as a base; this will normally result in an URL using the file-scheme -- or in real terms, "look for the image in the same directory you found the MP3 file in").

To quote from the randomly googled http://id3lib.sourceforge.net/id3/id3v2.4.0-frames.txt:

«Image format is the MIME type and subtype for the image. In the event that the MIME media type name is omitted, "image/" will be implied. The "image/png" or "image/jpeg" picture format should be used when interoperability is wanted. Description is a short description of the picture, represented as a terminated text string. There may be several pictures attached to one file, each in their individual "APIC" frame, but only one with the same content descriptor. There may only be one picture with the picture type declared as picture type $01 and $02 respectively. There is the possibility to put only a link to the image file by using the 'MIME type' "-->" and having a complete URL instead of picture data. The use of linked files should however be used sparingly since there is the risk of separation of files.»

Mellissa Ragusa on :

*I'm preparing to begin my blog soon, yet I'm a little lost on everything. Do you recommend starting with a complimentary system like WordPress or choose a paid option? There are numerous platforms out there that I'm totally puzzled. Love to hear recommendations? Many thanks a great deal.

Azundris on :

*Since I knew I had not included images when I ripped my own CDs, I did a quick survey checking free promotional freebies. Apparently, image-tags have caught on to a degree. And apparently, URLs really haven't.

167 JPG (76 with zero-length image, 22 tagged "JPEG")
026 BMP
004 GIF
001 PNG
001 Non-"other" type (0xb, "composer")
000 URL
000 media type missing ("png" i/o "image/png")

Azundris on :

*Detect all MP3s with image tags (using the id3info program):

find "/my/music" -print0|perl -n0e 'chop; $f=$_; $e="id3info ".chr(34).$f.chr(34); $r=`$e`; if($r =~ s/.*\n=== APIC (.*)\n.*/\1/m) { print "$f: $1\n"; }' > fancy_tags.txt

Monitor progress:

watch -n 45 "(wc -l fancy_tags.txt; echo; cat fancy_tags.txt|cut -d: -f4|cut -d, -f1|sort -u)"

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