Play a snippet from an avi file

I have a .avi file that is approximately 6 minutes of video. I need to be able to play only a snippet of it, after some data analysis is performed, for instance frame 2 to frame 30. My question, is there a function where I can specify the name of video file followed by frame numbers? I try to use mplay(filename), however it doesnt accept any other input parameters such as frame number. I am currently using a VideoReader to preallocate into a struct, then doing a movie2avi to create a smaller avi file and then doing a mplay(). This takes way to long to do at runtime.

Answer 1

[Jacob Mathew]

Hey ARWA,

While there isn’t a direct function that can achieve the functionality you are looking for, we can use a combination of VideoReader and implay() function in Video Viewer to achieve this.

The approach is to use the VideoReader object, which itself is lightweight, to track and read the frames of the video we need. Once we have the frames, we can pass them to implay(), along with the frame rate to play it smoothly.

The following code illustrates this appoach:

% Specify the path to your AVI file 
filename = 'sample.avi'; 
% Create a VideoReader object 
video = VideoReader(filename); 
% Define the range of frames you want to read 
startFrame = 30; 
endFrame = 90; 
% Calculate the total number of frames to read 
numFramesToRead = endFrame - startFrame + 1; 
% Preallocate a structure to store the frames 
frames(numFramesToRead) = struct('cdata', [], 'colormap', []); 
% Set the starting frame 
video.CurrentTime = (startFrame-1) / video.FrameRate; 
% Loop through and read the frames 
for k = 1:numFramesToRead 
    % readFrame automatically updates CurrentTime to the next frame 
    frames(k).cdata = readFrame(video); 
end 
% Play the frames as a video 
implay(frames,video.FrameRate); 

If the number of frames to be read is substantial, then you can replace for loop with parfor loop, which is parallel for loops to parallelise the reading of frames. You can refer to parfor loop documentation below:

https://www.mathworks.com/help/releases/R2024a/matlab/ref/parfor.html

Refer to the following for VideoReader documentation:

https://www.mathworks.com/help/releases/R2024a/matlab/ref/videoreader.html

Refer to the following for implay() function’s documentation:

https://www.mathworks.com/help/releases/R2024a/images/ref/videoviewer-app.html#buiat2d-4