Using ffmpeg to extract images is very slow

Question

I am using ffmpeg on my Mac. Version is 3.4.2.

I wanted images of a specific second of video and executed the following command.

ffmpeg -i sample.mkv -ss 100 -vframes 1 -f image2 %04d.png

This command took more than 1 minute to finish.
When I tried to take the image of the 1000th second, the response did not come back.

Is there something wrong with it?

Answer 1

Use demuxer seek i.e. -ss before the input.

ffmpeg -ss 100 -i sample.mkv -vframes 1 -f image2 %04d.png