How do I add a marker to only specific frames in a video

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Matthias Heuberger
Matthias Heuberger 2019-9-20
评论： Walter Roberson 2023-2-28
I would like to add a visual marker with a fixed position (e.g. top right corner) to my video that is only visible at specific frames. The frames during which I want the marker to be shown are saved in a vector.
  2 个评论
Geoff Hayes
Geoff Hayes 2019-9-20
Matthias - do you have an array/vector of all the frames? Do you know the indices or positions of the frames (to mark) relative to the larget set?
Matthias Heuberger
Matthias Heuberger 2019-9-22
Yes, I have an array with all the frames and I know the indices of the frames to mark.

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Kavya Vuriti
Kavya Vuriti 2019-12-5
Hi,
As you know the indices of frames to mark, you can use readFrame function to read those frames from video and then use insertMarker function to add marker to the frame at specific position. If you want to add markers to frames with indices 2, 4 and 6, your code will look something like this:
% Create object to read video
v = VideoReader('xylophone.mp4');
% Frames to which marker must be inserted
markFrames = [2 4 6];
frameidx = 0;
videoPlayer = vision.VideoPlayer;
while hasFrame(v)
% Read next video frame
frame = readFrame(v);
frameidx = frameidx + 1;
% Check if index of frame is to be marked or not
if any(ismember(markFrames, frameidx))
markedFrame = insertMarker(frame, [50 50]);
videoPlayer(markedFrame);
else
videoPlayer(frame);
end
end
Hope this helps.
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Walter Roberson
Walter Roberson 2023-2-28
It is more efficient to writeVideo several frames at a time.
Most efficient if you have the memory would be to read the entire video, replace selected frames with the marked versions, and write out everything in one call.
Walter Roberson
Walter Roberson 2023-2-28
My understanding is that the video writing library that MATLAB uses is not the most efficient library, so you might be able to improve performance by using a C++ interface or using loadlibrary() to talk to an external library.

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