When trimming a WMV file using the following syntax:
ffmpeg -i 'INPUTFILE.wmv' -acodec copy -vcodec copy -ss 00:00:45 -t 00:00:15 'OUTPUTFILE.wmv'
One frame of the OUTPUTFILE.wmv file is displayed for about the first second or two (during which time the sound plays normally), and then playback resumes. The "frozen frame" that is displayed is the one on which motion actually begins (not the one 1-2 seconds preceding it) -- that is, there is no "jump" as it goes from the frozen frame to the working video. Instead, it's like I'm un-pausing the video.
Even if I bump the length of the output clip up to one minute long, it still displays it for about a second (so it's not a proportion of the total length of the video).
What is causing this, and how can I fix it?