What version of AE? What exact render settings? You need to be more specific.
Thanks for replying.
Render settings were best quality, H264 @ 25fps, with AAC audio. H264 settings were the default quality though. chaging this made no difference except for the visual quality. I've rendered this out about 8 times and also tried a second video from CamStufio and its always way off. I double checked the preview on screen and its exact to the position it should be on the video, so something seems to be happening during render.
I played with another file - an ancient QuickTime .movie at 30 fps and it upscaled to full HD and came out fine.
AE is CS6 version. I've tried to give all the relevant details but please let me know if you need any specific detail.
Really baffled by this and thanks for the help.
Finally worked this out.
I rendered out the entire file that was displaying incorrectly as a lengthy image sequence - it had just under 11,000 frames and the run time was 9.09. Simple maths reveals that this means the real framerate was 5.62 fps not the 20fps that was reported by every program that runs it. Setting the 'Interpret footage' to the correct value then made the footage render perfectly in a 25fps comp.
The process withe the frame sequence was necesary as I did not have a correct figure for the real framerate and only knew that it was playing MUCH faster (approximately four times) the speed it should have. It seems the framerate flag on the file was set incorrectly, yet the file still previews in AE and plays on YouTube and VLC correctly which is a bit odd. My method is a very clunky way to find the solution but an option if you have similar problems. Obviously the quality of the frames is not important, as the true goal is simply to learn the total frame number, so you could output a frame sequence with tiny resolutions to save time and disk space. As it was, it only took a few minutes to render almost 11,000 frames at quarter HD resolution.
Hope this is of use to you.
Edit: the realtime framerate was also visible in the footage screen when doing a preview, so the frame output method is not needed once you know this figure.