Video resize (save video from frame)

Hi all, How can I save the video "example.mp4" in this code?

vidobj = vision.VideoFileReader('example.mp4')
viewer = vision.DeployableVideoPlayer;
videoFWriter = vision.VideoFileWriter;
numFrames = 0;

    while ~isDone(vidobj)
              A = step(vidobj);  
              viewframe = imresize(A,0.5);
              step(viewer, viewframe);
              numFrames = numFrames + 1;
    end

Answer 1

[Image Analyst]

OK, after a couple of postings it looks like you're having trouble figuring it out. So, here's a full demo for how to resize a video. Change the output size to whatever you want.

% Demo to extract frames from a input video, resize them, and build a new movie of a different size.
% Illustrates the use of the VideoReader and VideoWriter classes.
% A Mathworks demo (different than mine) is located here http://www.mathworks.com/help/matlab/examples/convert-between-image-sequences-and-video.html

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
imtool close all;  % Close all imtool figures.
clear;  % Erase all existing variables.
workspace;  % Make sure the workspace panel is showing.
fontSize = 22;

% Open the rhino.avi demo movie that ships with MATLAB.
% First get the folder that it lives in.
folder = fileparts(which('rhinos.avi')); % Determine where demo folder is (works with all versions).
% Pick one of the two demo movies shipped with the Image Processing Toolbox.
% Comment out the other one.
inputFullFileName = fullfile(folder, 'rhinos.avi');
% movieFullFileName = fullfile(folder, 'traffic.avi');
% Check to see that it exists.
if ~exist(inputFullFileName, 'file')
  strErrorMessage = sprintf('File not found:\n%s\nYou can choose a new one, or cancel', inputFullFileName);
  response = questdlg(strErrorMessage, 'File not found', 'OK - choose a new movie.', 'Cancel', 'OK - choose a new movie.');
  if strcmpi(response, 'OK - choose a new movie.')
    [baseFileName, folderName, FilterIndex] = uigetfile('*.avi');
    if ~isequal(baseFileName, 0)
      inputFullFileName = fullfile(folderName, baseFileName);
    else
      return;
    end
  else
    return;
  end
end

% Open up the VideoReader for reading an input video file.
inputVideoReaderObject = VideoReader(inputFullFileName)
% Determine how many frames there are.
numberOfFrames = inputVideoReaderObject.NumberOfFrames;
inputVideoRows = inputVideoReaderObject.Height
inputVideoColumns = inputVideoReaderObject.Width

% Create a VideoWriter object to write the video out to a new, different file.
outputFullFileName = fullfile(pwd, 'NewRhinos.avi');
outputVideoWriterObject = VideoWriter(outputFullFileName);
open(outputVideoWriterObject);
% Specify the output video size.
shrinkFactor = 4; % Shrink by a factor of 4 in both directions.
outputVideoRows = round(inputVideoRows / shrinkFactor)
outputVideoColumns = round(inputVideoColumns / shrinkFactor)

numberOfFramesWritten = 0;
% Prepare a figure to show the images in the upper half of the screen.
figure;
%   screenSize = get(0, 'ScreenSize');
% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]);

% 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);
  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
% Close the output video object.  You don't need to close the input video reader..
close(outputVideoWriterObject);

%================================================================================
% NOW WE'RE DONE!
%================================================================================

% Show input frame and output frame side by side:
subplot(1, 2, 1);
image(thisInputFrame);
axis on;
axis image;
caption = sprintf('Input Frame: %d rows by %d columns', inputVideoRows, inputVideoColumns);
title(caption, 'FontSize', fontSize);
% Show the smaller output frame.
subplot(1, 2, 2);
image(outputFrame);
axis on;
axis image;
caption = sprintf('Output Frame: %d rows by %d columns.', outputVideoRows, outputVideoColumns);
title(caption, 'FontSize', fontSize);

% Alert user that we're done.
finishedMessage = sprintf('Done!  It processed %d frames of\n"%s" and created output video\n%s.\nClick OK to see the output video.', numberOfFramesWritten, inputFullFileName, outputFullFileName);
fprintf('%s\n', finishedMessage); % Write to command window.
uiwait(msgbox(finishedMessage)); % Also pop up a message box.
% Play the movie.
winopen(outputFullFileName);

%================================================================================
% OPTIONAL: OPEN THE NEW VIDEO TO DOUBLE-CHECK/PROVE ITS SIZE.
% Open up the VideoReader for reading an input video file.
inputVideoReaderObject = VideoReader(outputFullFileName)
% Determine how many frames there are.
numberOfFrames = inputVideoReaderObject.NumberOfFrames;
inputVideoRows = inputVideoReaderObject.Height;
inputVideoColumns = inputVideoReaderObject.Width;
fprintf('The output video has %d rows and %d columns.\n', inputVideoRows, inputVideoColumns);
%================================================================================

[Anthony Griffin]

This is such a complete answer! Very helpful :-)

Answer 2

[Walter Roberson]

step(videoFWriter, viewframe);