NerVik

ffmpeg -i video1.mp4 -c copy -bsf h264_mp4toannexb video1.ts

ffmpeg -i "concat:video1.ts|video2.ts|" -c copy -bsf:a aac_adtstoasc video_done.mp4

ffmpeg -filter_complex aevalsrc=0 -loop 1 -i black.png -t 5 out.mp4

ffmpeg -i in.mp4 -c copy -bsf h264_mp4toannexb out.ts

ffmpeg -i "concat:in1.ts|in2.ts|in3.ts|in4.ts" -c copy -bsf aac_adtstoasc out.mp4