MATLAB: I keep trying to convert a video grayscale but it gives me an error

gray scaleImage Processing Toolboxvideo processing

hi, i want to convert a video into grayscale, but it keeps giving me an error, specifically a "parse_input" error
my code:
%Create a multimedia reader video
readerobj = VideoReader('yourvideo.mp4', 'tag', 'myreader1');
readerobj.Width 
readerobj.Height
% Read in all video frames.
vidFrames = read(readerobj);
% Get the number of frames.
numFrames = get(readerobj, 'NumberOfFrames');
%creat an output video file
v = VideoWriter('peaks.avi');
%Set the output video framerate to the input frame rate
v.FrameRate = readerobj.FrameRate;
open(v);
% Create a MATLAB movie struct from the video frames.
for k = 1 : numFrames
     %get a frame from the video
     frame=vidFrames(:,:,:,k);
     
     
     frame = rgb2gray(frame);
     
     %write the frame to the output video file
     writeVideo(v,frame);
     
     %add the frame to a movie object
     mov(k).cdata = frame;
     mov(k).colormap = [];
     
     
     
     %if you want to save the frame
     %Create Filename to store
     
     
end
%close the output video file. This will finish writing he video file
close(v);
% Create a figure
hf = figure; 
% Resize figure based on the video's width and height
set(hf, 'position', [150 150 readerobj.Width readerobj.Height])
% Playback movie once at the video's frame rate
movie(hf, mov, 1, readerobj.FrameRate);

Best Answer

Instead of rgb2gray(), use read() and pass it the frame number. Should look something like this:
% Loop through the movie, writing all frames out.
for frame = 1 : numberOfFrames
	% Extract the frame from the movie structure.
	thisInputFrame = read(inputVideoReaderObject, frame);
	
	% Display it
	image(thisInputFrame);
        if ndims(thisInputFrame) == 3
            thisInputFrame = rgb2gray(thisInputFrame);
        end
	axis on;
	axis image;
	caption = sprintf('Frame %4d of %d.', frame, numberOfFrames);
	title(caption, 'FontSize', fontSize);
	drawnow; % Force it to refresh the window.
	
	% Resize the image.
	outputFrame = imresize(thisInputFrame, [outputVideoRows, outputVideoColumns]);
	
	% Write this new, resized frame out to the new video file.
	writeVideo(outputVideoWriterObject, outputFrame);
	
	% Update user with the progress.  Display in the command window.
	progressIndication = sprintf('Processed frame %4d of %d.', frame, numberOfFrames);
	disp(progressIndication);
	% Increment frame count (should eventually = numberOfFrames
	% unless an error happens).
	numberOfFramesWritten = numberOfFramesWritten + 1;
end
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