Each video player supports different formats and within those different formats there are different settings in relation to resolution, bit rate and audio.
You need to read your manual carefully and see exactly what format and settings you need to encode the video at. A populat one is: mp4 container, H264 video at 320x240 resolution, 720kpbs. AAC audio at 48kbps.
You usually get software with the players to convert video files to the right specification