processframe.m

mmread.m是matlab官方网站上公布的一个函数

function processFrame(data,width,height,frameNr,time)
% processFrame(data,width,height,frameNr)
%
% This is the function prototype to be used by the matlabCommand option of
% mmread.
% INPUT
%   data        the raw captured frame data, the code below will put it
%               into a more usable form
%   width       the width of the image
%   height      the height of the image
%   frameNr     the frame # (counting starts at frame 1)
%   time        the time stamp of the frame (in seconds)
%
% Warning, the way that this is implemented requires buffering about 1
% seconds worth of video.  If you don't have enough memory in your system
% to hold 1 second's worth of video, this will crash on you.  Either make
% your movies smaller, or buy more memory.
% 
% EXAMPLES
%   Process all frames in a movie using this function:
%   mmread('mymovie.mpg',[],[],false,false,'processFrame');
%
%   Process only frames 1 through 10 using this function:
%   mmread('mymovie.mpg',1:10,[],false,false,'processFrame');

persistent warned;

try
    scanline = ceil(width*3/4)*4; % the scanline size must be a multiple of 4.

    % some times the amount of data doesn't match exactly what we expect...
    if (numel(data) ~= scanline*height)
        if (numel(data) > 3*width*height)
            if (isemtpy(warned))
                warning('mmread:general','dimensions do not match data size. Guessing badly...');
                warned = true;
            end
            scanline = width*3;
            data = data(1:3*width*height);
        else
            error('dimensions do not match data size. Too little data.');
        end
    end

    % if there is any extra scanline data, remove it
    data = reshape(data,scanline,height);
    data = data(1:3*width,:);

    % the data ordering is wrong for matlab images, so permute it
    data = permute(reshape(data, 3, width, height),[3 2 1]);
    % the images are also upside down and colors were backwards.
    data = data(end:-1:1,:,3:-1:1);


    % now do something with the data...
    image(data);
    title(['frame ' num2str(frameNr) ' ' num2str(time) 's ']);
    drawnow;

% stop early
%     if (frameNr == 10)
%         error('processFrame:STOP','STOP!!!');
%     end
    
catch
    % if we don't catch the error here we will loss the stack trace.
    err = lasterror;
    disp([err.identifier ': ' err.message]);
    for i=1:length(err.stack)
        disp([err.stack(i).file ' (' err.stack(i).name ') Line: ' num2str(err.stack(i).line)]);
    end
    rethrow(err);
end