brew install ImageMagick
ffmpeg -ss 14:55 -i video.mkv -t 5 -s 480x270 -f image2 %04d.png
- -ss 14:55 gives the timestamp where I want FFmpeg to start, as a duration string.
- -t 5 says how much I want FFmpeg to decode, using the same duration syntax as for -ss.
- -s 480x270 tells FFmpeg to resize the video output to 480 by 270 pixels.
- -f image2 selects the output format, a series of still images — make sure there are leading zeros in filename.