VLC won’t take snapshots on Debian 9 “Stretch”

If you are experiencing this problem, it appears to be due to a bug specific to the VDPAU driver. Unfortunately, VLC gives no obvious error to indicate the snapshot was not taken (if it works, you should see a message briefly showing where the image was saved to). The work around is to simply change the video decoder method. Go to Tools -> Preferences, then select Input / Codecs at the top of the dialog, and change the setting for Hardware-accelerated decoding from Automatic or VDPAU video decoder to VA-API video decoder via X11 (or DRM).

https://askubuntu.com/questions/769585/vlc-cant-take-snapshots-anymore-due-to-corrupt-vdpau-video-surface-error