# trim video file to a certain range of frames
ffmpeg -i render0000-28914.mp4 -vf select="between(n\,0\,61),setpts=PTS-STARTPTS" one.mp4

# display number of frames in a video file
ffmpeg -i one.mp4 -f null /dev/null

# add audio to video file at the start and extend the audio to the end of the video with silence
ffmpeg -i one.mp4 -i electricity-zap.mp3 -filter_complex "[1:0]apad" -shortest test.mp4

# add audio to video file and leave audio length as is, -stream_loop will loop the audio faster than the video with this file
ffmpeg -i one.mp4 -i electricity-zap.mp3 -map 0:v -map 1:a -c:v copy test.mp4

# loop a file a number of times into one long file
ffmpeg -stream_loop 500 -i test.mp4 -c copy 500_loops.mp4

# add multiple audio files to video at defined millisecond times of the video file
ffmpeg -y -i video.mp4 -i 002.ogg.mp3 -i 003.ogg.mp3 -i 004.ogg.mp3 -filter_complex "[1]adelay=1000:all=1[s1];[2]adelay=2500:all=1[s2];[3]adelay=4000:all=1[s3];[s1][s2][s3]amix=inputs=3:normalize=false[a]" -map 0:v -map "[a]" -preset ultrafast video_with_audio.mp4

# add one audio file multiple times to video at defined millisecond times of the video file
ffmpeg -y -i video.mp4 -i 002.ogg.mp3 -filter_complex "[1]adelay=1000:all=1[s1];[1]adelay=2500:all=1[s2];[1]adelay=4000:all=1[s3];[s1][s2][s3]amix=inputs=3:normalize=false[a]" -map 0:v -map "[a]" -preset ultrafast video_with_audio.mp4