From a brief look at FFMPY, you could do this using ffmpy.FFmpeg, as that allows any and all FFMPEG command line options, including -f. -- Click the link for documentation.

You could do the FFMPEG command with os.system. You'll need to import OS anyway to iterate through the files.

You would need to iterate through all the files in a directory though. This would be the more challenging bit, it's quite easy with a for loop though.

for filename in os.listdir(path):
    if (filename.endswith(".mp4")): #or .avi, .mpeg, whatever.
        os.system("ffmpeg -i {0} -f image2 -vf fps=fps=1 output%d.png".format(filename))
    else:
        continue

The above code iterates through the directory at path, and uses command prompt to execute your given FFMPEG command, using the filename (if it's a video file) in place of mymovie.avi

Considering that pyFFmpeg is just a wrapper over the libraries, I'd say you shouldn't have any negligible performance difference between the 2, since they use the same libraries at the core.