Create a new audio file extension and read it using phonon

[wysota]

My Own format is just to don't let other players able to read it(client's specifications)

If someone really wants to, he will read your files. If someone doesn't care, he won't try. Security through obscurity is usually a bad idea.

in this case, can i make phonon able to read it ?

Phonon will not help you much here as the whole advantage of using Phonon is that it takes the burden of decoding the file from you. Since you need to write your own decoder anyway, playing the file is the least of your problems.

is it a lot of work to create a special format (for example inherited from mp3) and make my program able to read it ?

I don't know what you want to "inherit" from mp3. File format is one thing, media codec is another. I really suggest you become familiar with the topic before you start tackling with the problem.