Play instruction

I have a problem for file extension.conf.
exten => s,6,BackGround(demo-instruct) ; Play some instructions

I wish to replace the file demo-instruct with my own instruct file. how can I do it? which codec and file format is supported for asterisk playback function ?

GSM - codec/format.
There are convertors - taext2wave, as part of festival, which could convert text to wave.You can use directly wav file, but you can also covert wave file in GSM format.


I really appreciate it if you can provide certain links to such convertors.