50 frames

#!/bin/bash
TotalFrames=$(ffprobe -v error -count_frames -select_streams v:0 -show_entries stream=nb_read_frames -of default=nokey=1:noprint_wrappers=1 $1)
    echo "Total Frames: $TotalFrames"

duration=$(ffprobe -v error -show_entries format=duration -of default=noprint_wrappers=1:nokey=1 $1)
    echo "duration: $duration"

fps=$( bc <<< "$TotalFrames/$duration" )
    echo "fps: $fps"

selectTotal1=$( bc <<< "$TotalFrames / 100" )
    echo "Select Total 1: $selectTotal1"

selectTotal2=$( bc <<< "$selectTotal1*2" )
    echo "Select Total 2: $selectTotal2"

seekCount=$( bc <<< "$TotalFrames/($selectTotal2+50)");
    echo "seekCount: $seekCount"


for i in $( seq 1 $(( $seekCount -1 )) ); do \
    skipFrames=$( bc <<< "$i*($selectTotal2+50)" )
    skipTime=$( bc <<< "$skipFrames/$fps" )
    ffmpeg -ss $skipTime -i $1 -vframes 50 \
        -c:v h264 -crf 30 -preset ultrafast -pix_fmt yuv420p \
        -c:a libopus -b:a 128k -vbr on \
        -y $i-50frames.mkv
done