moviepy save_frame ignores time information

Question

I want to use moviepy to open a mp4 file and save a png.

Unfortunately it is only saving the first frame, no matter what time information I provide.

Here is my code:

 def video_create_thumbnail(filename):
    from moviepy.editor import VideoFileClip
    clip = VideoFileClip(filename)
    clip.save_frame("staticfiles/videothumbs/frame.png", 12.00)

I also tried t="12", t="00:00:12" and so on.

Any clues?