Media Player is pretty selective about what clips it will play. MPlayer will play many clips that Media Player refuses. The MPlayer discussion and download link is here. Your videos may have the wrong fourcc. I use a fourcc of "DIVX" with good results. Using a divx codec does not guarantee the output file will have a fourcc of "DIVX" I've seen "DX50" and "FMP4" fourcc's even though the video data is equivalent. Also, Media Player refuses to play videos with heights or widths that are not multiples of 16. MPlayer is not affected by either of these limitations.