burning downloaded video files

Hi all, I've been using a PC for many years, and find it and the Internet wonderful inventions, (I'm from the time of Crystal Radios!)
However, just recently I have hit a conundrum. For years I've been downloading movies from various sites, and when i have them, I 've been converting them to .avi files, to burn to disc then play them on my television. The programmes I have mainly used are A-Shampoo and Burn Aware. Recently, I find that both of these programmes don't recognise my files, wanting instead 'dvd-video files' My question is, why, suddenly, is there a change and how do I get my videos burned?
Any and all help will be appreciated. Halen, from South Oz.