Ipor Sircer's answer is sufficient and perfect but let me write a step by step answer for beginners.
Install mpv. In Ubuntu, you can execute this command.
sudo apt update && sudo apt install mpv
Visit mpv-thumbnail-script releases page and download
Copy these lua scripts to
~/.config/mpv/scripts/. The directory may not exist by default.
Just following these steps, without any further configurations and with
--osc=no option[*], the feature of the thumbnail seek is turned on. However, please note that the feature is automatically disabled when you play a video whose length is over an hour. You can again enable the feature by pressing
Shift+t on the player or change the setting. As for the latter case, see mpv-thumbnail-script Configurations or execute
echo "autogenerate_max_duration=0" >> ~/.config/mpv/lua-settings/mpv_thumbnail_script.conf.
[*]: You can instead execute
echo "osc=no" >> ~/.config/mpv/mpv.conf once.
If you feel it takes much time to generate thumbnails, you can turn on multi-threading. It is quite easy. See again mpv-thumbnail-script Configurations. In my case, it really works well.
My test environment:
$ lsb_release -d
Description: Linux Mint 19 Tara
$ mpv --version
mpv 0.27.2 (C) 2000-2017 mpv/MPlayer/mplayer2 projects
(Japanese AGMPlayer for Ubuntu also worked on the same environment, though this wasn't stable.)