Video converts less than half way

I have finally been able to successfully convert a video into .avi with subtitles displaying, yet any video I try converting ends up incomplete. My video lengths are 23 minutes and I usually only get an .avi that runs 7-9 minutes. I have tried using both the converting software that my M6 came with and also viDrop on separate occasions. Both cut my converted videos short. Does anyone know why this is happening and how I can fix this?