ffmpeg - extend last video frame duration

I needed this last week and will probably need it again soon, so here's a public note to myself.

Again ffmpeg proves his strengths.

Count frames:

ffprobe -v error -count_frames -select_streams v:0 -show_entries stream=nb_read_frames -of csv=p=0 test.mp4

Outputs video frames count - for example:

Extract last frame - zero-indexed (or really any frame):

ffmpeg -i test.mp4 -vf "select='eq(n\,124)'" -vsync 0 -vframes 1 frame.png

Make 2 sec (or desired time -t) video from frame:

ffmpeg -loop 1 -i frame.png -c:v libx264 -t 2 -pix_fmt yuv420p -vf "fps=30" frame_video.mp4

Create a files.txt files that contains list of files concat:

touch files.txt
echo "file 'test.mp4'" >> files.txt
echo "file 'frame_video.mp4'" >> files.txt

Concat videos from files.txt into a single output video:

ffmpeg -f concat -safe 0 -i files.txt -c copy output.mp4

Last frame of output.mp4 video now lasts for 2 seconds at the end.

There's maybe a better way to do it, but I found this useful enough for myself and adjusting the commands allows for flexibility, if other frames are to be extended in duration.