i rendered a video file from after effects so i can make add some transitions to it in adobe premiere.used the razor tool to cut where the transition would be placed but the effect just appears black.i now noticed that its bcos its a single file.how can i add transition to a single video file.

Generally, you can't, because there must be an overlap for you to be able to see the transition. A razor does not create an overlap of "handles." Roll the adjacent ends you created back by at least 15 frames each, then snug them up together and try again.

thanks a lot but been trying to do as you said but not understanding properly.not really a pro at it.thanks

Look here: Adobe Premiere Pro CS5 & CS5.5 * Transition overview: applying transitions (http://help.adobe.com/en_US/premierepro/cs/using/WSE2A9B838-1422-4d8a-9A03-CFDF4332533B.html)

If you just razor a single clip you can't see a transition because you are transitioning from one thing to the same thing. So just use two different clips.

Or take your single clip and razor it in two places. Delete the middle part and push the two pieces together. Then try your transitions.

to be honest.i have been battling with this issue all day long.it is actually a 3min music video clip.since adobe AE doesnt recognise transitions so i have decided to re add them in premiere pro.still no progress.i did go with your advice but sometimes it pulls the audio too.should i unlink the audio from video?

If you're doing a music video you should be cutting picture separately from music. Place your music on the audio track and then lock the track. Then cut your picture.