ffmpeg choose exact frame from long film strip - ffmpeg

Question

I'm working with ffmpeg to choose the better thumbnail for my video. and the selection would be based on the slider.
as per the requirement multiple thumbnails not needed just a single long film image and with the help of slider select the thumbnail and save it.
i used below command to get the long strip thumbnail.
ffmpeg -loglevel panic -y -i "video.mp4" -frames 1 -q:v 1 -vf "select=not(mod(n\,40)),scale=-1:120,tile=100x1" video_preview.jpg
I followed the instructions from this tutorial
I'm able to get the long film image:
This is working fine, they moving the image in slider which is fine.
My question is how can I select a particular frame from that slider / film strip. How can I calculate the exact time duration from the slider and then execute a command to extract that frame?

Answer 1

In one of my project I implemented the below scenario. In the code where I'm getting Video duration from the ffmgpeg command, if duration is less than 0.5 second than I set a new thumbnail interval for the same. In your case you should set time interval for the thumbnail creation. Hope this will help you.
$dur = 'ffprobe -i '.$video.' -show_entries format=duration -v quiet -of csv="p=0"';
$duration= exec($dur);
if($duration < 0.5) {
$interval = 0.1;
} else {
$interval = 0.5;
}
screenshot size
$size = '320x240';
ffmpeg command
$cmd = "ffmpeg -i $video -deinterlace -an -ss $interval -f mjpeg -t 1 -r 1 -y $image";
exec($cmd);

Answer 2

You can try this:
ffmpeg -vsync 0 -ss duration -t 0.0001 -noaccurate_seek -i filename -ss 00:30 -t 0.0001 -noaccurate_seek -i filename -filter_complex [0:v][1:v] concat=n=2[con];[con]scale=80:60:force_original_aspect_ratio=decrease[sc];[sc]tile=2x1[out] -map [out]:v -frames 1 -f image2 filmStrip.jpg
2 frame