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I have some time series data that I would like to create into movies. The data could be 2D (about 500x10000) or 3D (500x500x10000). For 2D data, the movie frames are simply line plot using plot, and for 3D data, we can use surf, imagesc, contour etc. Then we create a video file using these frames in MATLAB, then compress the video file using ffmpeg.

To do it fast, one would try not to render all the images to display, nor save the data to disk then read it back again during the process. Usually, one would use getframe or VideoWriter to create movie in MATLAB, but they seem to easily get tricky if one tries not to display the figures to screen. Some even suggest plotting in hidden figures, then saving them as images to disk as .png files, then compress them using ffmpeg (e.g. with x265 encoder into .mp4). However, saving the output of imagesc in my iMac took 3.5s the first time, then 0.5s after. I also find it not fast enough to save so many files to disk only to ask ffmpeg to read them again. One could hardcopy the data as this suggests, but I am not sure whether it works regardless of the plotting method (e.g. plot, surf etc.), and how one would transfer data over to ffmpeg with minimal disk access.

This is similiar to this, but immovie is too slow. This post 3 is similar, but advocates writing images to disk then reading them (slow IO).

hyiltiz
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maybe what you're trying to do is to convert your data into an image by doing the same kind of operation that surf, or imagesc or contour is doing and then writing it to a file directly, that would keep all the data in the memory until writing is needed.

I had little experience with real images that could also work here: I saw that calling imshow took lot of time, but changing the CData of a presetted figure created by the imshow function took around 5ms, so, maybe you could set a figure using any of the function you like, and then update the underlying XData, YData etc. so that the figure will update in the same fashion?

best of luck!

HagegeR
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  • Can't believe you actually dug this almost dead post up. Nice! Have you tried implementing your suggestion to see if it works? – hyiltiz Feb 25 '18 at 03:35