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March 29, 2009

wmartagu: Viewer/editor for WMA metadata info

Filed under: Blog — krkhan @ 11:05 am

As part of a Google Summer of Code application challenge, I was required to code an application for which the check-list was:

  • Accepts 1 WMA file name on the command line
  • Accepts -a for artist
  • Accepts -t for title
  • Removes the current tag from a WMA
  • Writes a new tag to the WMA file containing the new artist & title

And the bonus points:

  • The program does not obliterate the existing tag but merges the new information
  • The program is robust and does not destroy any of the test WMA files
  • The program does not emit any compile warnings during build
  • The program is UTF-8 clean

Consulting the ASF specification, my first attempt to code the application resulted in wmartag.c. However, since the last bonus point wasn’t present in the list at the time, the program didn’t support UTF-8 (and used hand-tweaked dirty functions for converting between ASCII and low-endian UTF-16). After I found out about the bonus goal, I reimplemented the program from scratch and renamed it to wmartagu. The new code relies on GLib for character code conversions which really does work like a charm:

[krkhan@orthanc wmartagu]$ make

make wmartagu
make[1]: Entering directory `/home/krkhan/Desktop/wmartagu’
cc -Wall -g `pkg-config –cflags –libs glib-2.0` wmartagu.c -o wmartagu
make[1]: Leaving directory `/home/krkhan/Desktop/wmartagu’

[krkhan@orthanc wmartagu]$ ./wmartagu O\ Fortuna.wma

Title: O Fortuna
Author: Carl Orff

Copyright:
Description:
Rating:

[krkhan@orthanc wmartagu]$ ./wmartagu -t ɹǝqɯǝʇdǝs O\ Fortuna.wma

Title: ɹǝqɯǝʇdǝs
Author: Carl Orff

Copyright:
Description:
Rating:
Tags updated successfully.

[krkhan@orthanc wmartagu]$ mplayer -v -v -v O\ Fortuna.wma

MPlayer SVN-r28461-4.3.2 (C) 2000-2009 MPlayer Team
CPU: Intel(R) Core(TM)2 CPU T5600 @ 1.83GHz (Family: 6, Model: 15, Stepping: 2)

Playing O Fortuna.wma.
ASF file format detected.
[asfheader] Audio stream found, -aid 1
Clip info:
name: ɹǝqɯǝʇdǝs
author: Carl Orff

===================================================
Opening audio decoder: [ffmpeg] FFmpeg/libavcodec audio decoders
AUDIO: 44100 Hz, 2 ch, s16le, 192.0 kbit/13.61% (ratio: 24002->176400)
Selected audio codec: [ffwmav2] afm: ffmpeg (DivX audio v2 (FFmpeg))
===================================================
AO: [pulse] 44100Hz 2ch s16le (2 bytes per sample)
Video: no video
Starting playback…
A: 3.3 (03.3) of 153.0 (02:33.0) 0.4%

MPlayer interrupted by signal 2 in module: play_audio
A: 3.3 (03.3) of 153.0 (02:33.0) 0.4%
Exiting… (Quit)

This does not go without saying that if you do try to tackle the UTF character encodings without using any libraries, may God have mercy on your soul, because Unicode won’t. Also, “wmartagu” simply means “WMA Artist/Title Tagger with UTF-8 support” and does not — as it would lead one to otherwise assume — represent any noble African philosophy such as Ubuntu.

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