Scripting VLC to capture the first frame of a video - cannot get command line to work

I am creating a script to pull a video from the internet, create an image of the first frame, and save the image as a file. My script handles capturing a lot of videos and gives the filenames a sequential number.

My problem is using VLC to capture the video and actually save the file. Experimenting with command line and local file only, before I put it in my script I tried:

vlc -vvv -I dummy --video-filter=scene --start-time=1 --stop-time=1 --scene-format=jpeg --scene-ratio=24 --scene-prefix=EXEC samp.mp4 vlc://quit

      

        
        
        
      

    

-> thrown exception

vlc -vvv -I dummy --no-audio --video-filter=scene --start-time=1 --stop-time=1 --scene-format=jpeg --scene-ratio=24 --scene-prefix=EXEC samp.mp4 vlc://quit

      

        
        
        
      

    

-> thrown exception

vlc -vvv -I rc --video-filter=scene --start-time=1 --stop-time=1 --scene-format=jpeg --scene-ratio=24 --scene-prefix=EXEC samp.mp4 vlc://quit

      

        
        
        
      

    

-> uncaught exception; it looks like I can't do without the -V option

vlc -vvv -I rc -V snapshot --video-filter=scene  --start-time=1 --stop-time=1 --scene-format=jpeg --scene-ratio=24 --scene-prefix=EXEC samp.mp4 vlc://quit

      

        
        
        
      

    

-> no display module vout matches "snapshot"; similarly for attempts with the module "image", "scene", "opengl"

I am running VLC 2.0.1 on Mac OS X 10.7.3. Has anyone got VLC to work on the command line (so it can be scripted) to capture images from videos?

By the way, I did an extensive search on this subject - the VLC documentation is hopelessly out of date and most of the suggestions on the internet don't actually work with the latest version of VLC.