How to record live video with a buffer?

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Mark Golberg 2016-2-15

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https://ww2.mathworks.cn/matlabcentral/answers/268206-how-to-record-live-video-with-a-buffer

评论： Walter Roberson 2016-2-24

Hello, I have the following problem. I want to record the 1st second of real time video <-- that's my buffer. Now, I'd like to display in my GUI (1/10, which is actually 100 msec) of my buffer data. Repeat it 10 times. At the same time, I'd to record a new 2nd second to fill in the buffer. My question is, how can I simultaneously display data on in the GUI (pulling from the buffer), and recording new data (pushing to the buffer)?

I want to do this, so my Real Time Display would look smooth as new data coming in.

THANKS

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Answer 1

Walter Roberson 2016-2-15

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Have you considered using the computer vision toolbox? You can step() your video acquisition device to get a frame and in the same cycle step your video output to display a frame, potentially a frame you recorded earlier.

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Walter Roberson 2016-2-15

No I cannot help with that. I would need to know the wiring diagrams of your computer and I would need to do a bunch of studying to figure out whether it is even possible for your system to truly handle multiple interrupts at literally the same time. The last operating system I studied delegated interrupt handling to a single CPU, making truly simultaneous device handling impossible. (Which reminds me that you have not indicated which operating system you are using, or the number of cores you have available... or whether the external devices are on their own busses... or whether you are communicating with the devices by USB or GigE or PCIx or ...)

The most I could offer would be to show how to run the acquisitions in different processes, which is something that would probably slow the approach down due to the time needed to communicate the data between processes. The more convenient way of handling this would be with the Parallel Computing Toolbox; we do not know if you have that. Calling out to a mex routine that uses one of the thread libraries is possible, but not always straight forward.

Mark Golberg 2016-2-22

Thanks again Walter. I am using Windows 7. Have 8 cores CPU. Camera is connected via USB 3. I do have Parallel Computing Toolbox, but how exactly it can help solve my problem?

I think I need something like the spmd function. But instead of running single statement on multiple cores, I need to run 2 different statements, each one should run on it's own core.

I don't mind it to be 100% simultaneous, by the split of a second, I am simply trying to reduce my run time.

At the moment my process is the following (running in loop):

1. I grab 1 second of data from usb camera.

2. I process this data.

3. I display the outcome on my GUI.

It takes the above steps 1-3 too long to execute (~1.5 seconds), making my GUI display NOT smooth. Thus I'd like to work through a buffer, making the "reading frames part" as if I am reading from file. Which I know can run quite smoothly.

Walter Roberson 2016-2-24

在 MATLAB Online 中打开

parpool(2,'local')
spmd
  if labindex == 1
     for Number_of_times = 1 : 15
       for framenum = 1 : 10
         frames(:,:,:,framenum) = get a frame
       end
       labSend(2, frames);   %send it to the other proccess
     end
  else  %labindex must be 2
     for Number_of_times = 1 : 15
       frames = labReceive(1);
       ... do some calculation on the frames
       ...
     end
  end
end