You can find plenty of software that can do that – both paid and free.
If you don’t mind using commands in the console, I can highly recommend FFMPEG (https://ffmpeg.org – free and cross platform).
After you installed it, you can use a command like this (check out the documentation for tons of options and variations): ffmpeg -i “yourvideofile.mp4” “frame-%%03d.png”
This will produce a numbered sequence of png files, you can easily import into Animation Paper.
It is a bit technical, but it isn’t that difficult. And FFMPEG has sooo many capabilities.
And again, soon you will be able to just import video directly into Animation Paper.