Insert elements into a 4D array

Question

Alber 2020-4-9

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/516635-insert-elements-into-a-4d-array

回答： Srivardhan Gadila 2020-4-12

采纳的回答： Srivardhan Gadila

在 MATLAB Online 中打开

Hello,

I have a 4-dimensional buffer called:

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

in which I want to insert 3-dimensional video frames (width, height, numChannels). The variable framesPerSymbol is the number of frames that will go in the buffer, that is, if framesPerSymbol is 10, my buffer will be 10.

And this is where I run it:

frameBuffer = zeros(width, height, numChannels,framesPerSymbol);
framesInBuffer = 0;
while hasFrame(videoObject)
    frame = readFrame(videoObject);
    shiftBuffer(frameBuffer,frame);       % <--------- THIS IS THE PART
    % We update the framesInBuffer counter
    framesInBuffer = framesInBuffer + 1;
    if framesInBuffer > framesPerSymbol
        framesInBuffer = framesPerSymbol;
        bypassEncoding = false;
    else
        bypassEncoding = true;
    end
end

The way I was doing the insert was like this, but I don't get results:

function [] = shiftBuffer (frameBuffer,frame)
N = size(frameBuffer,4);            % Buffer size
for i = 1:N
    frameBuffer(i) = frame;
end

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Answer 1

Srivardhan Gadila 2020-4-12

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/516635-insert-elements-into-a-4d-array#answer_425514

在 MATLAB Online 中打开

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;

to

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