Video Processing

I have a video of extending liquid. I need to be able to record the thickness of the liquid at the center (where it is necking) as a function of time. Does anyone know how to go about this in matlab. I would really appreciate the help. I was thinking someway of using the canny edge detection, but I can't figure out how to use this for videos.

[Image Analyst]

Post a few frames from the video somewhere, such as tinypic.com. I can make better suggestions on image processing if I see an actual image. One way might be to get a better image to begin with. It is almost always easier to do image processing if you've done everything in advance to get a good image, rather than trying some mathematical gymnastics to try to fix up a bad image. If Canny works you just extract the frame from the video and then operate on it as a regular image.