Hi,
I have a lot of small mp3 file, and I like to build one big, depending on a visitor request.
For example, the script shoud take "blue.mp3" (2s), "red.mp3" (1s) to produce "blue-red-blue.mp3" (5s), made of blue + red + blue successively.
Is it possible?
Thanks.

I don't know about using MP3 files, but I had once ran across a php captcha script that combines audio wav files for an audible download. This might give you a starting point in doing that:

http://bokehman.com/captcha_verification

You obviously will have to use some command line utility on your server, like ffmpeg, to do it. In this case you need ffmpeg installed and exec() allowed.

Thanks! I'll try...