Why is my phone's frame rate so damn slow on all video media player apps?

My phone sucks! I have a galaxy prevail by boost mobile and when I download torrents and try to play them on my phone the frame rate is so slow. The audio works fine but the videos go in slow mo on every app I try qq player, arcmedia, vplayer. Someone help what the hell do I do. All I can think of is the files I torrent are to big for my phone. I watch mainly avi files