downloading old movies from youtube using freemake

[bingcro2]

ive dowloading several old films(mainly black and white ones) using freemake.It converts them to avi files.some of the films work on my portable dvd player.Others produce comment" format not supported".What am i doing wrong as some work and some dont.should i try different formats.ive tried coverting to mp4 but this gets same comment format not supported.