translating a French film into English: problem adding subtitles

[wwfcfan]

Hi everyone.

I am sorry if this question has been asked before, but I am desperately in need of some help. I am trying to translate a French film into English for some clients and we have realised that to add subtitles to the video we will need some way of downloading it; however, because the file is too big and it's the FLV format I won't be able to do it. I have emailed the director and asked for his permission so there's no worries on that front. However he says that to add subtitles to the film, it's necessary to view it in the DV AVI format. Is there a way to add some kind of "tool" to Firefox so that I can do this and edit it before saving the altered version without downloading the other version? Or will I have to find some other way of doing it?

I told my clients that I would have the film ready in two weeks and I'm really worried that now I won't be able to do it at all! I'm sorry if this question has been asked a million times but I'd really appreciate being helped out here or if someone can give me some pointers