Capturing all frames with VLC scene-filter

I'm attempting to use VLC's scene-filter to extract *all* frames from an mp4 video. The video in question runs at 25fps, and is precisely 38s long. In the command line, I ran with options: --video-filter = scene --start-time = 0 --stop-time = 35 --scene-ratio = 1 I understood (?) that the scene ratio is the ratio of frames taken from total frames (that is, a ratio of 3 means 1/3 frames are saved). However, of the ~900 frames I'm expecting, I get only about 500 of them. I've tried using 25, -1, and the default scene-ratio values, to no avail. What am I doing wrong? The VLC docs aren't very clear about this.