PHP and audio

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I'd like to convert mp3's and possibly other audio formats into AAC, and clip/trim the audio file.

 

Should i use CGI for this or the exec() and pass the file to another program in the server that will do this?

 

Never really touched exec() but have heard horrible things about it.

 

Or is it possible to do this via PHP alone?

 

And, how can i check to verify the file is either mp3 (or WAV, for example)? Trying to check beyond the extension here. (i use exif_imagetype for images..wondering how to get the same kind of verification with audio)

 

thanks.