I have HYUNDAI MP4 player and had same problem.He has ROCHCHEP inside and that SMV convertor that was going together with player is no good.My player play just AVI files with224x176 resoulution and sound must be mp2.viDROP did that all for me.He can even put subtitle in file.Theare is opion to chose othe cheps if your player have some other.
viDrop - free open-source converter for RockChip players