Help With Thumbnails

Hello- I have searched for 2 days for a plug in to display videos- this is very close to working for me
However I have 2 issues
1- Videos are not showing thumbnails. I have ffmpeg installed on my server however I have also installed it here at the path you show in the UI
public.html//Applications/ffmpegX.app/Contents/Resources/ffmpeg
Still I cannot get thumbnails to work?
2- The gallery is only displaying 5 videos-but I need more. i see no setting in the UI that allows to set the number of videos displayed
However I see you can use “limit” in the shortcode to set this. I am new to WP and do not fully understand how to write the short code- can you show me an example of short code for limit=25?
Thank you