How to record .asx files

I was hoping to find some help on this issue. I am trying to take
an .asx file and convert it to .mp3. The problem is is that I need to
use the information encoded in the .asx file to determine when to
start recording and when to end recording (otherwise, I would just
take an off the shelf program to convert the files). For example, many
of the audio files don't start having sound until about 15 minutes
into the file so obviously I don't want to record the file until the
audio actually starts. An example is from: http://biz.yahoo.com/cc/. I
would need to do a batch conversion of multiple files. How would I do
this in PERL?