Hello Subhash,
There currently is no functionality in MATLAB for the creation of rosbag files. However, you could load the messages from your MAT file into MATLAB, and publish them on a ROS network with a rospublisher. Then you could use a non-MATLAB ROS node to subscribe to the messages, and create a rosbag there. You could even do it with the Linux VM that we provide for your convenience.
If you would like to get the frames from a video (AVI) file, and save those to a MAT file, you can easily do that without ROS at all. See this example for reading all the frames, then simply save the variable with the data to a MAT file.
-Cam
