"Quality" property of VideoWriter object doesn't do anything. How to get higher quality mp4 video?
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I'm trying to encode an animation as a video, using MATLAB 2017b. The frames of my animation are in struct F, which is produced earlier with getframe inside a loop.
The documentation for VideoWriter says, under the quality property,
Video quality, specified as an integer in the range, [0,100]. Higher quality numbers result in higher video quality and larger file sizes. Lower quality numbers result in lower video quality and smaller file sizes.
Quality is available only for objects associated with the MPEG-4 or Motion JPEG AVI profile. After you call open, you cannot change the Quality value.
Fair enough. This is what I'm trying:
V = VideoWriter(myfilename, 'MPEG-4');
V.FrameRate = 5;
V.Quality = 85;
However, regardless of what value I set V.Quality to, it produces exactly the same (heavily compressed) video with exactly the same filesize. This setting seems to be ignored.
Is this a bug? If not, then what am I doing wrong? Either way, how can I produce a higher-quality compressed video? (ideally using mp4/H.264, not M-JPEG etc, as I want it to be widely playable)
Lucademicus on 30 Dec 2019
A solution would be to write the video as uncompressed avi, and invoke ffmpeg to compress it to mp4.
I've tested this code in R2019b on Windows and on Ubuntu
%% some example from VideoWriter doc
Z = peaks;
axis tight manual
%% video file
if isunix % for linux
pathVideoAVI = '~/someVideo.avi'; % filename, used later to generate mp4
elseif ispc % fow windows
pathVideoAVI = 'd:\someVideo.avi'; % filename, used later to generate mp4
writerObj = VideoWriter(pathVideoAVI,'Uncompressed AVI');
%% animate and write AVI
for k = 1:20
frame = getframe(gcf);
close(writerObj); % Close the movie file
%% convert AVI to MP4
pathVideoMP4 = regexprep(pathVideoAVI,'\.avi','.mp4'); % generate mp4 filename
if isunix % for linux
[~,~] = system(sprintf('ffmpeg -i %s -y -an -c:v libx264 -crf 0 -preset slow %s',pathVideoAVI,pathVideoMP4)); % for this to work, you should have installed ffmpeg and have it available on PATH
elseif ispc % for windows
[~,~] = system(sprintf('ffmpeg.exe -i %s -y -an -c:v libx264 -crf 0 -preset slow %s',pathVideoAVI,pathVideoMP4)); % for this to work, you should have installed ffmpeg and have it available on PATH
Of course you could finish this by removing the AVI file.
More Answers (3)
Bjorn Gustavsson on 29 Jan 2019
It used to be so that movie2avi and VideoWriter didn't bother with the quality setting on Linux-machines - perhaps that's what you're running into. In my opinion the way to produce the movies with the best control on all settings is to write each frame as an image and then use something like mencoder, ffmpeg or some other standalone program to do that. Another problem might be that the frames grabed with getframe were too small - getframe just grabs a pix-map so its quality is sensitive to the physical size of the frame on-screen. Not much help, but maybe something...