This job is better handled by Mocha AE as it is a planar tracking system. However, you can do it in Premiere Pro. You need to add the Corner Pin effect and then manually key frame.
Hope this helps,
thanks for the reply,the corner pin seems to be the best but it the video quality is distorted to the maximum,why is this?is there a solution?
The quality of the source footage will determine how the result looks. If you are starting with FLV, what you are seeing might well be as good as it gets. PrPro has fair Interpolation alogrithms, but the pale to those in AE and in PS for stills.
Alternatively, if you have a 3D program (even a trial version) you could model the screen very quickly and add the video as a map. Then render out the video or stills with alpha channels and it's done.