read videos in Matlab

Question

Abdussalam Elhanashi 2019-11-2

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/488862-read-videos-in-matlab

编辑： Abdussalam Elhanashi 2019-11-5

采纳的回答： Subhadeep Koley

在 MATLAB Online 中打开

Hi Guys

I wantt help fpr following code instade of reading the frames of videos i want to read video as normal playing

load('Detector.mat');
vidReader = VideoReader('004.avi');
vidPlayer = vision.DeployableVideoPlayer;
i = 1;
results = struct('Boxes',[],'Scores',[]);
while(hasFrame(vidReader)) 
I = readFrame(vidReader); 
step(vidPlayer,I);
 i = i+1;

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Answer 1

Subhadeep Koley 2019-11-5

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https://ww2.mathworks.cn/matlabcentral/answers/488862-read-videos-in-matlab#answer_399873

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Hi, your code is almost correct only you have add some pause() between every frame otherwise you won’t be able to see all the frames. The pause time should be ideally 1/FrameRate for viewing the video in its original speed. Refer to the code below.

vidReader = VideoReader('rhinos.avi'); % Read your video here
vidPlayer = vision.DeployableVideoPlayer;
while(hasFrame(vidReader))
    I = readFrame(vidReader);
    step(vidPlayer,I);
    pause((1/vidReader.FrameRate)); % pause of value (1/FrameRate)
end

Or else if you only want to play the video you can use the function implay().

implay('rhinos.avi'); % Read your video here

And hit the ‘Play’ button.

Hope this helps!

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Abdussalam Elhanashi 2019-11-5

编辑：Abdussalam Elhanashi 2019-11-5

在 MATLAB Online 中打开

Thanks Subhadeep Koley Just asking how can implement the this code in fact i am doing an object detection with R-CNN and i want to calculate the frame rate

load('Detector.mat');
vidReader = VideoReader('vn_002_00.avi');
vidPlayer = vision.DeployableVideoPlayer;
i = 1;
results = struct('Boxes',[],'Scores',[]);
while(hasFrame(vidReader)) 
I = readFrame(vidReader); 
 % PROCESS
    [bboxes, scores, label] = detect(detector,I,'MiniBatchSize', 128);
    
 % Select strongest detection 
% New - Find those bounding boxes that surpassed a threshold
T = 0.58; % Define threshold here
idx = scores >= T;
% Retrieve those scores that surpassed the threshold
s = scores(idx);
% Do the same for the labels as well
lbl = label(idx);
bboxes = bboxes(idx, :); % This logic doesn't change
for ii = 1 : size(bboxes, 1)
    annotation = sprintf('%s: (Confidence = %f)', lbl(ii), s(ii)); % Change    
    I = insertObjectAnnotation(I, 'rectangle', bboxes(ii,:), annotation); % New - Choose the right box
end
step(vidPlayer,I);
 i = i+1;
end
 results = struct2table(results);
 release(vidPlayer);

Subhadeep Koley 2019-11-5

In your code, the variable vidReader.FrameRate contains the frame rate of the video read by VideoReader.

Abdussalam Elhanashi 2019-11-5

编辑：Abdussalam Elhanashi 2019-11-5

Hi Subhadeep Koley thanks for your comment how can i calculate the frame rate per second for object detection when i play the video because when i got the deployable video player it does not show f / s

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