Video play back

i have a sony walkman nwz-s615fblk. trying to put some video on it. short clips and animation comesout fine but i am getting picture overlap and pixilation when itry to put live action video on it. i used aprogramto tweek the audio quality and image quality but it doesnt change. i turned the video quality down to 5 fps and a sample rate of 56kbs and it was still choppy.. help please