If you are wanting to record what is coming in on your scanner via computer, connect your headphone jack (or line out if so equipped) on your scanner and the line-in jack on your computer’s soundcard with a cable with a 1/8” male plug on either end (stereo or mono depending on your exact application, in my case I‘m using mono on the scanner end and stereo on the computer end)
Then using any one of a number of soundcard recording programs you are ready to roll. Most programs that I’ve run into save the recording as a .wav file so for mp3’s you will have to run it through a conversion program (dBpoweramp music converter is a good one)
As far as recording programs go most will record only when there is audio present so the long silences between transmissions are eliminated. You can get a whole nights worth of scanning listened to in in 20 minutes or so depending on traffic volume. So far, I have had the best luck with Xcorder
http://www.softpedia.com/progDownload/x-Download-7210.html
It has a feature that automatically starts a new recording each hour which helps in limiting file size. (It’s also free) RecAll, VoxRecorder, and ScanRec are also all good.
Hope this helps,
MS