I was thinking in the line of making sure the number of frames per second set in the animation time domain setting is the same as the frames per second in the capture dialog. 25 or 30 frames per second is considered a normal frame rate to see continuous action.
Also, if you capture as an AVI, it should be a frame-at-a-time capture. You can upload AVI to you tube and download the MP4 afterward.
The same capture dialog works for mechanism analysis. I was just wondering if you had trouble with capturing the analysis as well.
If is likely that there is some level of incompatibility with your Windows codecs. I get lost when it comes to these things. I can only suggest that to date, my MPEG captures from Creo have not been an issue.
What version are you on and do you have current maintenance? It might be good to have a support tech have a look at your output MPEG file.