MATLAB: How can we use ‘SPMD’ for ‘VideoReader’

parallel computingspmd

hi, I want to do do some video quality reduction fastly, I am using parallel computing , but this error is coming: 'Cannot call READ method after using READFRAME or HASFRAME methods or setting the CURRENTTIME property. Recreate the object to read a frame at a specific frame index'

my code is

videoSrc = VideoReader('rhinos.avi');
% v = VideoWriter('newfile.avi');
% open(v)
spmd 
        if labindex==1
            v = VideoWriter('newfile.avi');
open(v)
            for sr = 1:700
              huo = read(videoSrc,sr);
              RGB2 = imresize(huo, [300 NaN]);
          writeVideo(v,RGB2)
  % waitbar(sr / videoSrc.NumberOfFrames)
              end
              close(v)
        else
          R = rand(4,4);
          end
  end

Best Answer

Use readFrame() instead of read(). I'd also recommend building the videoSrc on the worker.

spmd
    if labindex==1
        videoSrc = VideoReader('rhinos.avi');
        for ii = 1:700
            if hasFrame(videoSrc)
                huo = readFrame(videoSrc);
            else
                break
            end
        end    
    end
end

Related Solutions

MATLAB: How does labindex in spmd works

P = parpool(4); creates four processes. All four of them start executing the same block of code, with nearly the only difference between the processes being that if they call labIndex they will get different results from 1 to 4.

All four of the processes will begin executing at the same time, without waiting for anything. They will not wait for input.

As soon as any of the processes has nothing left to do, it will go into a "waiting to exit" state and will not participate in any further work except to help collect the outputs when the last of the labs exits. This applies even if another lab specifically does labSend() to it.

If your workers interact, then it is common to write the smpd block in terms of "for" or "while" loops. You can use either design pattern:

spmd
    for K = 1 : whatever
        if labIndex == 1
            something
        elseif labIndex == 2
            something else
        end
    end
end

spmd
    if labIndex == 1
        for K = 1 : whatever
            something
        end
    elseif labIndex == 2
        for K = 1 : whatever
            something else
        end
    end
end

The second of those is more common, as it permits the different labs to have different varieties of work.

The way to get a lab to wait for work is to have the lab execute labReceive() or labBarrier()

There is no clock and no enable port being used here. Each of the labs is a different process that runs as quickly as it can, and the different labs do not try to synchronize until you use labSend() / labReceive(0 or labBarrier(), or until they finish.

MATLAB: Logging parellel pool worker diaries to single file

Instead of parfor, you could use parfeval to run stuff on the workers. This will require a bit of restructuring - you'll need to divide up your work into decent-sized chunks (this is something that parfor takes care of for you automatically). Then, you can use the Diary property of each parallel.Future instance.

For example

% request execution on a worker  
f = parfeval(@() fprintf('worker diary text: %d\n', rand()), 0);
wait(f), f.Diary

Best Answer

Related Solutions

MATLAB: How does labindex in spmd works

MATLAB: Logging parellel pool worker diaries to single file

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