MATLAB: Enter values into a FIFO array

array fifobufferfifofifo queueframeMATLAB and Simulink Student Suitequeuereadframeshiftbuffervideoobject

Hello,

I have an array called

frameBuffer = zeros (height, width, numChannels, framesPerSymbol);

and a video. The parameters of the frameBuffer are height, width, number of color channels and framesPerSymbol, which will be the number of frames that my symbol lasts.My goal is to insert frames of the video in the array as if it were a FIFO queue, that is, if framesPerSymbol is 5:

F = frames E = empty

1) E E E E E

2) F E E E E

3) F F E E E

4) F F F E E

5) F F F F E

6) F F F F F

Thanks in advance.

Best Answer

I think you are trying to save last five frames in a buffer, but a for loop is not required for that purpose

frameBuffer=zeros (height, width, numChannels, framesPerSymbol);
framesInBuffer = 0;

While loop

while hasFrame(videoObject)
    frame = double(readFrame(videoObject));

I made a change here

    frameBuffer = shiftBuffer(frameBuffer,frame);  
    framesInBuffer = framesInBuffer + 1;

    if framesInBuffer > framesPerSymbol
        framesInBuffer = framesPerSymbol;
        bypassEncoding = false;
    else
        bypassEncoding = true;
    end
    if ~bypassEncoding
        if canWeEncode(frameBuffer,alpha,threshold)    
            encodedBuffer = steganographicEncoding(frameBuffer,width,height,codeRows,codeCols,alpha,sigma);
            writeBufferToFinalVideo(encodedBuffer,100);
        else                                        
            writeFrameToFinalVideo(squeeze(frameBuffer(:,:,:,1)));
        end
    end
end

and a change here

function frameBuffer = shiftBuffer (frameBuffer,frame)
frameBuffer = circshift(frameBuffer,1,4); 
frameBuffer(:,:,:,1) = frame;
end

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MATLAB: Insert elements into a 4D array

There are 2 mistakes in the above implementation:

Accessing a frame of frameBuffer as frameBuffer(i) instead of frameBuffer(:,:,:,i)
The function shiftBuffer changes the values of frameBuffer locally in the function and in the main code the frameBuffer isn't changed.

I suggest you to make the following changes.

Change the function shiftBuffer as follows:

function frameBuffer = shiftBuffer(frameBuffer,frame,framesInBuffer)
frameBuffer(:,:,:,,framesInBuffer) = frame;
end

and the following lines in your code

frame = readFrame(videoObject);    
shiftBuffer(frameBuffer,frame);       % <--------- THIS IS THE PART
% We update the framesInBuffer counter

framesInBuffer = framesInBuffer + 1;

frame = readFrame(videoObject);
% We update the framesInBuffer counter
framesInBuffer = framesInBuffer + 1;
frameBuffer = shiftBuffer(frameBuffer,frame,framesInBuffer);

MATLAB: Create a video from frames taken 5 by 5

Alberto - whenever you call writeBufferToFinalVideo the code creates a new VideoWriter, writes five frames to file, and then closes the file. I think that what is happening is that every time when the code creates the VideoWriter object for the prueba file, the file is being re-created and so all information previously written to it is lost. I was able to reproduce this by writing 20 frames to a file, then re-opening it to write five more frames...once close, the video file was smaller than before. What you may want to do is to create the video writer in the main file and then pass it as a parameter to the writeBufferToFinalVideo method.

frameBuffer = zeros(height,width,numChannels,framesPerSymbol);
framesInBuffer = 0;
% create the video writer object
video = VideoWriter('prueba','MPEG-4');
video.FrameRate = 100;
open(video);
while hasFrame(videoObject)
    frame = double(readFrame(videoObject));
    frameBuffer = shiftBuffer(frameBuffer,frame);
    % We update the framesInBuffer counter
    framesInBuffer = framesInBuffer + 1;
    
    if framesInBuffer > framesPerSymbol
        framesInBuffer = framesPerSymbol;
        bypassEncoding = false;
    else
        bypassEncoding = true;
    end
    if ~bypassEncoding
        if canWeEncode(frameBuffer,alpha,threshold)     % Frames with code
            encodedBuffer = steganographicEncoding(frameBuffer,width,height,codeRows,codeCols,alpha,sigma);
            writeBufferToFinalVideo(encodedBuffer,video);
        else                                            % Only Frames without code
            writeFrameToFinalVideo(squeeze(frameBuffer(:,:,:,1)));
        end
    end
end
% close the video writer object
close(video);

with

function [video] = writeBufferToFinalVideo(buffer,videoWriterObj)
for i = 1:size(buffer,4)
    img = buffer(:,:,:,i);
    img(img>1) = 1;
    img(img<0) = 0;
    writeVideo(videoWriterObj,img);
end
end

You will probably need to do the same for writeFrameToFinalVideo.

Best Answer

Related Solutions

MATLAB: Insert elements into a 4D array

MATLAB: Create a video from frames taken 5 by 5

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