Making Movies

Notes on how to get and use ffmpeg to make .mp4 movies from stacks of .png's

Krisen Thyng helped me with this. This is definintely the best tool I have found for making movies from model output. It works on my mac and my linux boxes, and can be automated as part of other code like python.

I think I already had it on my linux machine (fjord). On my mac I first had to get brew, using this command:

/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install.sh)"

then execute: brew install ffmpeg then "which ffmpeg" should give: /usr/local/bin/ffmpeg

As an example of how to use it, I put this alias in my .bashrc

alias make_movie='ffmpeg -r 8 -i plot_%04d.png -vcodec libx264 -pix_fmt yuv420p -crf 25 movie.mp4'

and here is a snippet from python code that calls it:

ff_str = ("ffmpeg -r 8 -i " + outdir + "plot_%04d.png -vcodec libx264 -pix_fmt yuv420p -crf 25 " + outdir + "movie.mp4")
os.system(ff_str)

these assume you have a folder full of .png plots with sequential names like plot_0001.png and so on. One quirk is that ffmpeg requires an even number of pixels in both directions. For some reason this is never a problem with matplotlib figures. When I had trouble with this in MATLAB I solved it with some formatting lines like:

set(gcf,'PaperPositionMode','auto');
set(gcf,'position',[100 100 1000.5 600]); % note the .5