Real time video retrieve from camera and simultaneous vehicle detection

Hello All, I am following the following link, for performing the vehicle detection and the distance measurement over a pre-saved Video! I have though implemented this, but I need to replace the pre-saved video with the real time data from the attached camera!

Now, this is what I am planning to implement: 1: Taking the webcam data and storing it in a variable (Implemented) 2: Taking the snapshot and implementing the process of vehicle detection and distance measurement. (Implemented) 3: Now, I want to process the whole video frame by frame.

Now, The part of the code responsible for showing the video is as follows: (Note: I have omitted the most of the code as they were irrelevant to this question)

    while (1)

        % Grab a frame of video
        frame = snapshot(cam);

        % Compute birdsEyeView image
    .......

        % Detect lane boundary features
        .....
        % Obtain lane candidate points in vehicle coordinates
        ........

        % Find lane boundary candidates
        ..........

        % Reject boundaries based on their length and strength
        ........

        % Classify lane marker type
    ......

        % Find ego lanes
        ......
        % Find candidate ego boundaries
        ......
        % Detect vehicles
        ......

        % Visualize sensor outputs and intermediate results. Pack the core
        % sensor outputs into a struct.
       ......

        % Pack additional visualization data, including intermediate results
        ...........

            snapshot = takeSnapshot(frame, sensor, sensorOut);
    end

    Display the video frame. Snapshot is taken at timeStamp seconds.

    if ~isempty(snapshot)
        figure
        imshow(snapshot)
    end

The error i am receiving is as follows:

   Function 'subsindex' is not defined for values of class 'struct'.

    Error in Final_Perception (line 379)
        frame = snapshot(cam);

Kindly compare this part with the part of the code as mentioned in the link above and help me rectify the error I am making in this.

In case you want, I can post the correct version of the code part used with pre-saved video.

Thank you. Regards