Friday, February 17, 2017

Converting video to high-quality gif on linux (via ffmpeg)

A brief post today. Recently, I've been taking videos of my screen and converting them to animated gifs.
The command I use to record the video, for example to record 15 seconds of video at 25 fps, sized 830x150 pixels at offset from the top of x=230,y=360 is:
avconv -f x11grab -y -r 25 -s 830x150 -i :0.0+230,360 -vcodec libx264 -crf 0 -threads 4 -t 15 myvideo.mp4

For a while I was using a one-liner to convert the video to animated gifs using ffmpeg and ImageMagick's convert command based on this post. Below it samples the mp4 at 15 fps.

ffmpeg -i myvideo.mp4 -r 15 -f image2pipe -vcodec ppm - | convert -delay 7 -loop 0 - gif:- | convert -layers Optimize - myvideo.gif

The problem I ran into was the the color palette choice in the gifs was poor and creating weird artifacts.

So I came across, which layed out another strategy, resulting in the following two commands:

ffmpeg -v warning -i myvideo.mp4 -vf "fps=25,palettegen" -y /tmp/pallette.png
ffmpeg -v warning -i myvideo.mp4 -i /tmp/pallette.png -lavfi "fps=25 [x]; [x][1:v] paletteuse" -y myvideo.gif

or, if you don't need to change the frame rate:

ffmpeg -v warning -i myvideo.mp4 -vf "palettegen" -y /tmp/pallette.png
ffmpeg -v warning -i myvideo.mp4 -i /tmp/pallette.png -lavfi paletteuse -y myvideo.gif

I found this approach much better. The color artifacts were gone and also the file sizes were much smaller! It chopped about 50-80% off of the file size compared to the previous ffmpeg/convert pipeline.

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