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Video compression code working - Please explain the code

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naveen V
naveen V 2014-5-5
评论： Walter Roberson 2022-11-26
ImFolder=uigetdir;
pngFile = dir(strcat(ImFolder,'\*.png'));
S = [pngFile(:).datenum];
[~,S] = sort(S);
pngFiles = pngFile(S);
VideoFile=strcat(ImFolder,'\Video');
writeObj = VideoWriter(VideoFile);
fps= 15;
writeObj.FrameRate = fps;
open(writeObj);
for t= 1:length(pngFiles)
Frame=imread(strcat(ImFolder,'\',pngFiles(t).name));
writeVideo(writeObj,im2frame(Frame));
end
close(writerObj);
Above is the code i have used to compress the video,
Execution Steps:
1) Initially i recorded a video of 10seconds(Resolution - 160*120) size of video 8mb
2) I extracted all the frames from the video and saved in a folder
3) In this step i used above code
After executing above code i selected the directory where all the frames had been stored
4) After execution i got a video file of size 550Kb and of the same length as the original video
So original video is reduced to 550kb from 8mb, code is working good for my project, please help me the analyze the above code, how actually the compression is done by the code.
Thank You
  11 个评论
显示 9更早的评论
Walter Roberson
Walter Roberson 2022-11-26
For video compression,
writeObj = VideoWriter(VideoFile, 'MPEG-4');
now writeVideo the frames.

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回答（3 个）

Walter Roberson
Walter Roberson 2014-5-5
http://www.mathworks.com/help/matlab/ref/videowriter-class.html
writerObj = VideoWriter(filename) constructs a VideoWriter object to write video data to an AVI file with Motion JPEG compression.
So it is going to use Motion JPEG in an AVI container.
kushagra parashar
kushagra parashar 2016-7-24
??? Undefined function or method 'VideoWriter' for input arguments of type 'char'.
Error in ==> Untitled at 7 writeObj=VideoWriter(VideoFile);
i am getting this error...what should i do
chandra sekhar uppu
编辑：Walter Roberson 2017-3-27
my video after expansion its size increases from 3 mb to 56 mb and its length increases from 1 min to 2 min the video has slow down.. i have used code
vid=VideoReader('w.mp4');
no=vid.NumberOfFrames;
for i=1:1:no
frames=read(vid,i);
base=sprintf('Image%d.png',i);
ful=fullfile(pwd,base);
imwrite(frames,ful);
im(i)=image(frames);
end
after i got frames i saved in a folder and apply this codee.. but i got 2 min and size of 50 mb
  2 个评论
Walter Roberson
Walter Roberson 2017-3-27
Notice that the code posted in the Question has
fps= 15;
writeObj.FrameRate = fps;
You should adjust that 15 to the rate you need.
With regards to the size: if you are creating a .mp4 output file then you should consider
writeObj = VideoWriter(VideoFile, 'MPEG-4');

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