Take a sequence of equispaced screenshots. You can configure the number of screenshots and the video fragment to which it will be applied (you can configure 100% of the video).
By default, the script is bind to "Ctrl + Alt + s"
By default the script takes 12 screenshots, change the variable "N" (line 9) to the number of screenshots you want. The variable "start" (line 10) defines the first screenshot, by default at 5% of the video. The variable "end" (line 11) by default 95% does not define exactly the last screenshot, this variable is used to define how often a screenshot is taken (step variable), so the last capture is at = end - step.
Put the script in your scripts folder (usually "~/.config/mpv/scripts/" or "%APPDATA%\mpv\scripts" in Windows).
Be sure to set the desired settings for the screenshot, in your configuration file (mpv.conf), https://mpv.io/manual/master/#screenshot.