OT: converting files to mpeg4

[Nigel Ridley]

I know this is not a Kubuntu specific question but I have searched all over the web and the 
DownloadHelper site:
Using Firefox and the DownloadHelper addon I am trying to convert some .flv fishing clips to 
mpeg4 to play on a Artech Portable DVD Player (it states that it can play mpeg4 videos). After 
trying several options in the DownloadHelper conversion menus I still cannot get the burnt CD to 
play in the Artech Portable DVD Player. It shows the files but on trying to play them it gives an 
error message about "Unsupported Format".
The problem is that there are too many options in the DownloadHelper menu :-(

Can somebody give some idea how to get it to play? I thought it would be easy.... How come 
something 'easy' is complicated?

Blessings and TIA,

Nigel