I'd do it with FFmpeg, which you can get through Homebrew, or alternatively ffmpegX.

In the first case, install Homebrew and then run brew install ffmpeg. This will require Xcode and building from source, which might be a bit of an overhead for your simple requirement.

In the second case, install the .app, and use the ffmpeg version bundled with it – however be advised that this version is from 2006, and therefore might not work with all input files.

/Applications/ffmpegX.app/Contents/Resources/ffmpeg

It worked for a h.264/MP4 clip for me.

Regardless, use FFmpeg to output each frame individually:

ffmpeg -i /path/to/video.mkv /path/to/output-%04d.jpg

You can also use png instead of jpg for lossless results, and change the number in %04d if you need more digits when the file is longer.

I found two ways (references: search results from discussions.apple.com)

1. [Better] Specific to VLC Media Player

   • Pause video at desired frame and from Menu bar select Video > Snapshot.
   • A vlcsnap-xxxx.png file of the current frame will get stored in ~/Desktop

   

2. Applicable to any video player application

   Use macOS's screenshot feature

   • Pause video at desired frame and hit ⌘ Command ⇧ Shift 5 to open screenshot overlay and in the hovering bar select 2nd option: Capture Selected Window [ ref-1 , ref-2 ]
   • after this click on your video-player window to grab screenshot of it's contents.

   

You should install ffmpeg : http://ffmpeg.org/download.html