thanks a lot fyr
the issue is not actually converting it, but adding a colored background before conversion without going into Flash CS4
the original .flv has a transparent channel which becomes 'black' in the output clip...
sorry, my bad. So your flv file already have an alpha channel. But you want to change the orignial color or because Flash changed it to black, then you have to try some other software to keep the orignial background color?
yes , my clip01.flv has an alpha channel, and I want to do clip01.flv + colored background => clip02.flv
I believe it can be done using Flash CS4, but I am not very fluent with it, and I'd like to know if there is any 'easy to use' software on the market to help me