videos not working

i have a mac and i downloaded ffmpegx and i convert the video size to 320x240 and the videos bitrate to 16 and i get it on to the meizu i open it and all it does is turn the screen balck for a second and then goes back to my videos .......the only 1 that works is the 1 it came with!!!!!hellppp!!pleasseeee
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also all the videos on the meizu have to be avi right so h0w do i convert mpg videos to avi


PLEASEEEE HELLPPPP MEE !!!!!!!