Recording Videos using two webcam simultaneously for 60sec

It takes 90sec to record video of 60sec when I am using two webcam simultaneously whereas it takes 60sec to record 60sec video when only one webcam is used. I want to record 60sec video in 60sec only using two webcams simultaneously. Can anyone help me with this The frame rate of both the webcam is 15fps. Here is my code.

if true
    clear all; %%clear all privious variables

      clc;

      %warning('off','all'); %.... diable warining msg ...;

      vid1 = videoinput('winvideo',1, 'YUY2_320x240');

      vid2 = videoinput('winvideo',2, 'YUY2_320x240');

      set(vid1, 'FramesPerTrigger', Inf);

      set(vid2, 'FramesPerTrigger', Inf);

      set(vid1, 'ReturnedColorspace', 'rgb');

      set(vid2, 'ReturnedColorspace', 'rgb');

      vid1.FrameGrabInterval = 1;

      vid2.FrameGrabInterval = 1;% distance between captured frames 

      start(vid1)

      start(vid2)

      aviObject1 = avifile('v7.avi');   % Create a new AVI file

      aviObject2=avifile('v8.avi')

      for iFrame = 1:900                    % Capture 900 frames

         % ...

         % You would capture a single image I from your webcam here

         % ...

         subplot(1,2,1);

         I=getsnapshot(vid1);

         imshow(I);

         subplot(1,2,2);

         J=getsnapshot(vid2);

         imshow(J);

         F = im2frame(I);                    % Convert I to a movie frame

         G = im2frame(J);

         aviObject1 = addframe(aviObject1,F);  % Add the frame to the AVI file

         aviObject2 = addframe(aviObject2,G);

      end

      aviObject1 = close(aviObject1);         % Close the AVI file

      aviObject2 = close(aviObject2);

      stop(vid1);

      stop(vid2);

      flushdata(vid1);

      flushdata(vid2);

 end

Answer 1

[Geoff Hayes]

Rohan - try to figure out where the delay is coming from. If you were to comment out the lines that convert the images to frames and then add them to the aviobject, what happens? Does it still take 90 seconds to write the 900 frames to file? For example,

 clear all; %%clear all privious variables
 clc;
 vid1 = videoinput('winvideo',1, 'YUY2_320x240');
 vid2 = videoinput('winvideo',2, 'YUY2_320x240');
 set(vid1, 'FramesPerTrigger', Inf);
 set(vid2, 'FramesPerTrigger', Inf);
 set(vid1, 'ReturnedColorspace', 'rgb');
 set(vid2, 'ReturnedColorspace', 'rgb');
 vid1.FrameGrabInterval = 1;
 vid2.FrameGrabInterval = 1;% distance between captured frames 
 start(vid1);
 start(vid2);

 % create cell arrays for the images from the two cameras
 vid1Images = cell(900,1);
 vid2Images = cell(900,1);

 for iFrame = 1:900                    % Capture 900 frames
     subplot(1,2,1);
     I=getsnapshot(vid1);
     imshow(I);
     subplot(1,2,2);
     J=getsnapshot(vid2);
     imshow(J);

     % save the images
     vid1Images{iFrame} = I;
     vid2Images{iFrame} = J;
 end

 % stop the video inputs
 stop(vid1);
 stop(vid2);

What is the performance like now? And since you have saved all of the images to the cell arrays, you can now convert them to frames and save them to file either using addframe or consider using the videowriter instead.

[rohan gupta]

Thankyou Sir , the problem is solved. Now I am able to record 60sec video in 60sec only. But I would like to know that since I am using inbuilt camera of my laptop and logitech c170 camera, so will there be any delay in recording video simultaneously may be in msec. If there is any delay then how can I over come it? so that there is not even a delay of millisecond between them

[Geoff Hayes]

The existence of a delay is probably a safe assumption, but since there are only 15 frames per second, I don't know why you are concerned with this delay.

[rohan gupta]

I am concerned with the delay because in my project even the small delay is not acceptable. I want to record the frames from both camera simultaneously and I fear that there may be some delay due to drivers of webcam. I think that if I use both webcams of same model ie. logitech c170 then the driver delay for both of them will be same and I'll be able to record the frames from both webcam simultaneously without any delay.

Correct me if I am wrong.

[Geoff Hayes]

If you manage to get 900 frames/images for each camera in exactly one minute, then it would seem that there is no delay. You running this shame test repeatedly should give you an idea as to whether there is a delay or not.

[rohan gupta]

Sir it taking less than one minute to capture the video. It now takes around 55sec to capture 900 frames eventhough the frame rate of both the webcam is 15 frames/sec. What could be the reason for this and how should I resolve it?

I have tried recording video using one webcam and it is taking only 45sec to record 1 min video ie 900 frames at the frame rate of 15 frames/sec.

[Geoff Hayes]

Rohan - you are capturing the same frame/image more than once. So either pause a certain fraction of a second between frame captures (1/15th of a second) or check the MATLAB docs to see if you can set up a trigger to fire every time a new frame is ready.