How can I write a set number of frames to a file using vision.VideoFileWriter and MATLAB R2015a?
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Robyn Hunt
on 13 Jul 2015
Commented: Walter Roberson
on 16 Jul 2015
The code involves reading a video file and rewriting the same video image into a new file with new audio samples (the total audio file has already been trimmed to the correct length). 'start_time' and 'total_time' are defined as inputs to the function, in seconds.
The audio part of the file writes perfectly, but I can't get the video output to match the indexed values I've specified. The video output is the correct length but always starts from index 0. Can anyone help? The relevant parts of my code are shown below.
videoreader = vision.VideoFileReader('input.mp4');
videowriter = vision.VideoFileWriter('output.avi', 'FileFormat', 'AVI',...
'AudioInputPort', true, 'FrameRate', videoreader.info.VideoFrameRate);
[y, fs] = audioread('input.wav');
a = round(start_time * videoreader.info.VideoFrameRate, 0);
b = round((start_time + total_time) * videoreader.info.VideoFrameRate, 0);
nSamples = round(fs/videoreader.info.VideoFrameRate, 0);
for i = a:b;
videoframe = step(videoreader);
step(videowriter, videoframe, y((nSamples*(i-a)+1):nSamples*(i-a+1)));
end
close(videoreader);
close(videowriter);
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Accepted Answer
Robyn Hunt
on 15 Jul 2015
Edited: Robyn Hunt
on 15 Jul 2015
1 Comment
Walter Roberson
on 16 Jul 2015
I don't see how that could make a difference compared to my suggestion, unless for some data flushing reason one further step() was needed after reading frame #b.
More Answers (1)
Walter Roberson
on 13 Jul 2015
I might be misunderstanding, but possibly
for i = 1:b;
videoframe = step(videoreader);
if i >= a
step(videowriter, videoframe, y((nSamples*(i-a)+1):nSamples*(i-a+1)));
end
end
3 Comments
Walter Roberson
on 15 Jul 2015
That does not seem possible. videowriter for Computer Vision uses system objects that overwrite the buffers each time. The first frame is going to be gone by the time "i" becomes as large as "a" for the first step() of the videowriter object.
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