You need to tell us much more detail:
-What is the framerate of your video
-What is the framerate of your timeline
-What is the framerate of your rendered video
-How do you know the video file is longer? What program is playing the video?
-How serious is the discrepancy? Is it a second longer or thirty?
That's the details worth knowing right off the bat.
Angelo Lorenzo
Fallen Empire - Digital Production Services
RED transcoding, on-set DIT, and RED Epic rental services.