I just tried something and I think I have narrowed down the problem in Poser. I rendered the same animation with sound and had the problem. when I cleared the sound and re did the animation it looked perfect...

So....it has to do with the audio in the video. I can get around it by clearing the sound then adding the sound file back to the video, but is there perhaps something I can do to render both sound and video without this happening?

I am rendering it full frame uncompressed. 

And thank you to the replies so far!