FFmpeg split and concat videos

gistfile1.txt

ffmpeg_concat() (
  test "$#" -lt 1 && return
  LISTFILE="`mktemp -p .`"
  printf "file '%s'\n" "$@" > "$LISTFILE"
  ffmpeg -f concat -safe 0 -i "$LISTFILE" -c copy concat.mp4
  rm "$LISTFILE"
)

# to split video into multiple segments based on key frames

# extract key frames at start of scenes
ffmpeg -i video.mp4 -vf "select='eq(n,0)+gt(scene,0.4)*eq(pict_type,PICT_TYPE_I)',scale=960:540" -fps_mode vfr scene-%02d.jpg

# -vf "select='eq(n,0)+gt(scene,0.4)*eq(pict_type,PICT_TYPE_I)',scale=960:540"
#   select: use the select filter
#     eq((n,0): select the first frame (frame 0)
#     + OR
#     gt(scene,0.4): select frames at the start of a scene change
#     * AND (takes precedence over OR)
#     eq(pict_type,PICT_TYPE_I): select only key frames
#   scale=960:540 scale to a lower resolution for faster frame browsing

# -fps_mode vfr
# use this for variable-bitrate (vbr) videos
# most videos will have variable bitrate

# alternative command line
ffmpeg -i video.mp4 -vf "select='eq(n,0)+gt(scene,0.2)',scale=960:540" -fps_mode vfr scene-%02d.jpg

# 0.2 delta is used here because when the video is scaled down, the delta values may sometimes decrease
# play around with smaller or larger values in order to extract scene changes more accurately

# to get frame numbers
ffmpeg -i video.mp4 -vf "select='eq(n,0)+gt(scene,0.2)',scale=960:540" -fps_mode vfr -frame_pts true frame-%03d.jpg

# in a directory full of frame-%03d.jpg files, we can make a simple list of frames to cut the original video into scenes
ls frame-*.jpg | sed -e 's,^frame-,,' -e 's,.jpg$,,' -e 's,^0*\([0-9]\),\1,' | (PREV=; while read i; do [ -n "$PREV" ] && echo $PREV $((i-1)); PREV=$i; done; echo $PREV) | while read a b; do [ -n "$b" ] && echo $a $(echo $a*0.04 | bc) $(echo $b*0.04 | bc) || echo $a $(echo $a*0.04 | bc) ; done > timestamps.txt

# to get only the frame numbers
ls frame-*.jpg | sed -e 's,^frame-,,' -e 's,.jpg$,,' -e 's,^0*\([0-9]\),\1,' | (PREV=; while read i; do [ -n "$PREV" ] && echo $PREV $((i-1)); PREV=$i; done; echo $PREV) > framenumbers.txt

# with the frame numbers, we can generate a list of timestamps for splitting the video
# the format is start_frame start_timestamp end_timestamp
cat framenumbers.txt | while read a b; do [ -n "$b" ] && echo $a $(echo $a*0.04 | bc) $(echo $b*0.04 | bc) || echo $a $(echo $a*0.04 | bc) ; done > timestamps.txt

# after we get the timestamps, we can split the original video file into scenes like this
cat timestamps.txt | (i=0; while read a b c; do i=$((i+1)); [ -n "$c" ] && ffmpeg -nostdin -i input.mp4 -ss $b -to $c -c:v copy -an -fflags +genpts scene-$i.mp4 || ffmpeg -nostdin -i input.mp4 -ss $b -c:v copy -an -fflags +genpts scene-$i.mp4; done)

# to get the timestamps
ffmpeg -i input.mp4 -vf "select='eq(n,0)+gt(scene,0.2)',scale=960:540,showinfo" -fps_mode vfr -f null /dev/null 2>&1 | grep pts_time


# to get i-frame (key frame) timestamps
# ffprobe -select_streams v -show_entries frame=pict_type,pts_time -of csv=p=0 -skip_frame nokey -i infile.mp4
# then split based on time, but minus one frame before the keyframes
# ffmpeg -i infile.mp4 -ss 123.45 -t 10s -c copy out.mp4
# make sure the -ss time is at least one frame prior to the keyframe (0.04s for 30 fps)