As many of you know MusicDNS is an acoustic fingerprinting service and a software development kit provided by MusicIP. The fingerprinting client library that looks up and identifies audio files based on existing fingerprints is called libofa. MusicBrainz has a great audio tagger called Picard which can tag audio files by querying this MusicDNS service.

There is, however, a simple problem. Picard is a GUI and thus doesn’t allow batch tagging of audio files from command line.

Hence I decided to write my own tool for generating acoustic fingerprints and for querying MusicDNS service. I’ve chosen to use libsndfile to do the decoding as libofa expects raw audio data. libsndfile is a C library for reading and writing files containing sampled sound through one standard library interface. It’s pretty easy to use and its API hides most of the low-level details from the programmer.

The tool is named afprint, released under GPLv2. Following the UNIX philosophy it just does one thing, calculation of acoustic fingerprint and duration of the given audio file.

Usage is simple:

alip@harikalardiyari> afprint -h
afprint-0.1.0-7b17577 audio fingerprinting tool
Usage: afprint [-hVv0] <infile>

Options:
    -h, --help      Display usage and exit
    -V, --version   Display version and exit
    -v, --verbose   Be verbose
    -0, --print0    Delimit path and fingerprint by null character instead of space
If <infile> is '-' afprint reads from standard input.
alip@harikalardiyari> afprint -v sample.ogg
[dump_print.294] Format: OGG (OGG Container format)
[dump_print.295] Frames: 2188368
[dump_print.296] Channels: 1
[dump_print.297] Samplerate: 44100Hz
[dump_print.298] Duration: 49735ms
[dump_print.302] essential frames: 5953500 > frames: 2188368, adjusting
sample.ogg 49735 ARaJDAgL...

afprint decodes the audio data using libsndfile and feeds it to libofa. It also calculates the duration of the audio file and prints them in format: FILENAME DURATION FINGERPRINT

Reading from standard input is tricky because pipes aren’t seekable thus it’s not possible to calculate the duration of the audio file. For this reason, when the audio data is fed via standard input, when <infile> is -, afprint saves this data into a temporary file and reads from it. This makes it possible to calculate acoustic fingerprints of Mp3 files, which libsndfile doesn’t support, easily.

alip@harikalardiyari> mpg123 -q --au - 01_san_francisco.mp3|afprint -v -
[wav.c:388] warning: Cannot rewind AU file. File-format isn't fully conform now.
[wav.c:388] warning: Cannot rewind AU file. File-format isn't fully conform now.
[dump_print.294] Format: AU (Sun/NeXT)
[dump_print.295] Frames: 8000111
[dump_print.296] Channels: 2
[dump_print.297] Samplerate: 44100Hz
[dump_print.298] Duration: 181820ms
/dev/stdin.au 181820 AQMZN...

Note the --au option passed to mpg123 as --wav doesn’t work.

So far so good, now we need a tool to query the MusicDNS server to find out the PUID of the audio file and query MusicBrainz to get the audio tags.

I’ve written a simple Perl script to do the job. The script, which has the name puidlookup, reads audio fingerprints from standard input and queries the MusicDNS server. Optionally it can query MusicBrainz as well to receive the tags.

Here are the requirements:

Usage is simple, just pipe afprint’s output to puidlookup.

alip@harikalardiyari> puidlookup -h
Usage: puidlookup [-hVv0]
    -h, --help          Display usage and exit
    -V, --version       Display version and exit
    -v, --verbose       Be verbose
    -0, --null          Expect input is null delimited
    -m, --musicbrainz   Look up PUIDs from MusicBrainz
                        (requires WebService-MusicBrainz)
    -l, --limit         Limit results to the given number
puidlookup reads filename, duration and audio fingerprint from standard input

The --null option responds to afprint’s --print0 option. These options are useful if filenames have spaces or other weird characters in it.

By default it only queries MusicDNS:

alip@harikalardiyari> afprint 04sheep.ogg | puidlookup
ARTIST='Pink Floyd'
TITLE='Sheep'
PUID=930806c1-e1e0-588a-b7de-2dacb1b8b11e

The --musicbrainz option can be used to query MusicBrainz:

alip@harikalardiyari> afprint 04sheep.ogg | puidlookup --musicbrainz
PUID=930806c1-e1e0-588a-b7de-2dacb1b8b11e
TRACKID=431a85dd-e22b-4626-91c9-c0abb8058d3f
ARTISTID=83d91898-7763-47d7-b03b-b92132375c47
ARTIST='Pink Floyd'
TITLE='Sheep'
TRACK=4
ALBUM='Animals'

The output is quoted so it’s safe to pass to eval, making it easy to integrate with shell scripts.

Last step is writing a tagger script to tag audio files. I’ve written a shell script called ofatag which uses envtag. It recognizes Mp3 files using the file command and decodes using mpg123, other formats are directly fed to afprint.

Now, to tag your files using MusicBrainz web services just do
ofatag /path/to/music/*.mp3 /path/to/music/*.ogg
etc.

I haven’t released a version yet because it’s all pretty new and needs testing. So please test it and report back! Any comments, thoughts, patches are appreciated.