I think both Matlab (license) and OpenCV (open source) are the good tools for Video and Image processing. You can also consider Octave (open source) being identical to Matlab, or Silab as well.
In my opinion, you should use the OpenCV with a lot of support functions for video and image processing, and all are open source. The Image processing toolbox of Matlab is great but you need the license :).
Matlab and OpenCV both can be used for image processing. Matlab is rich with function library but OpenCV has hardest only because there is no proper documentation and error handling codes. But OpenCV has lots of basic inbuilt image processing functions so that those who want to learn Image Processing can develop their applications through proper understanding about what they do. If you are looking for a free tool, then OpenCV is the more appropriate option to select. Other available tool is AForge.
if the time performance of the software is a critical factor (which I guess it is considering that you want to process a video with 120fps framerate) then you should go for OpenCV. It is free and you can choose the most appropriate API based on your programming skills (selecting among C++, Java or Python). Its online documentation (http://docs.opencv.org/3.1.0/#gsc.tab=0) is very helpful and detailed with a number of examples for the most common visual analysis tasks (e.g. local features extraction, face detection, object detection, optical flow estimation, background subtraction, etc.), that can be used as a basis for your implementations.
Some colleagues of mine also use the BoofCV (http://boofcv.org/index.php?title=Main_Page) library with good results, but I've never used it so I cannot provide any further comments about it.
One other thing you have to consider is the easiness of deployment of your final product. Matlab programs typically needs Matlab runtime for the execution where as openCV does not have such a problem. Therefore It is hard to come up with a neat standalone application which can be executed with a little configuration effort for the user. If it is a one time process then go with Matlab, surely it will require less amount of time for coding, debugging and fine tuning of the algorithm.