need help! cant play MP4s all the way


im trying to play mp4s on my rooted, MIUI running SGS I897. the issue is that the video will play then stop after about 3/4s of the way into any movie. the fix, supposedly, was posted here at xda Stagefright/Streaming Audio Fix Scripts to Enable/Disable on the Go - xda-developers

the solution is to use gscript to disable the build.prop stagefright something-or-other (im kind of a newb). anytime i try and run the script i get an error and there is no effect on the media issue.

i would REALLY appreciate any light that can be shed on the issue. please help!