Creating movies from IDL

[Updated, 21-Oct-2021]

For presentations or web-pages I often need to create movies from IDL showing, e.g., the evolution of a solar feature with time. This page explains how I do this.

You can make movies directly from IDL using the IDLffvideowrite object, and I give more information and an example on a separate webpage. The movie will generally not work through a web browser but it should be fine for a Powerpoint or Keynote presentation,

The alternative is to write out individual frames, and then use a separate software package to put the frames together to a movie. You used to be able to do this with QuickTime on the Mac, but not any more. My recommendation is to use ffmpeg.

Choosing a movie format (mp4 and webm)

The most common format is mp4 and this is generally recommended when you are making movies for presentations (Powerpoint, Keynote), but you have to be careful with the codec used. The best codec is "h.264" but IDL can not create a movie with it due to license restrictions. The default IDL codec is fine for presentations, but not if you want to embed your movie in a web browser.

The webm format is promoted by Google and it has the advantage of being royalty-free, thus movies can be created from IDL directly without any problem. The main disadvantage is that Apple's Safari browser does not support the format, so your webm movies embedded in a web page will not work.

I've created a webpage with the same movie created in webm and mp4 formats. You can use this to compare how embedded movies work with different browsers.

Using ffmpeg (Mac)

The ffmpeg package is not installed on Macs by default, and so you'll need to install it separately. I used Homebrew for this.

After you've written your image frames from IDL into files image0000.png, image0001.png, etc., then you can create an mp4 movie with:

> ffmpeg -r 15 -i image%04d.png -vcodec libx264 -pix_fmt yuv420p -crf 20 movie.mp4

Using "image*.png" seems to fail, so use %04d instead (%03d if you're using image000.png).

The option "-r 15" sets the frame rate to 15.

The option "-vcodec libx264" will give you a movie in the standard h.264 mp4 format, which means the movie should play on any web browser.

The option "-pix_fmt yuv420p" sets the pixel format to 3 colors and 12 bits per pixel (no need to change this!).

The option "-crf" controls the "lossiness" of the movie: 0 is lossless, 17 is "visually lossless", 23 is default, and 51 is worst quality.

Embedding the movie in html

To embed the movie in a webpage, you need to use the html5 video container. I suggest going to one of my webpages and viewing the page source for the video on this page to see how it works.

The option "controls" will display play and stop buttons when the movie is played, while "loop" makes the movie automatically loop.

Page maintained by Dr Peter R Young.