-vn: Remove video
-an: Remove audio
-c copy: Copy the original codec
-c:v: Video codec, such as libx264, libx265, libvpx
-c:a: Audio codec, such as aac, libopus, libmp3lame
-b:v: Video bitrate
-b:a: Audio bitrate

Re-encode

ffmpeg -i input.mp4 -c:v libvpx-vp9 -c:a libopus -b:a 6k output.webm

Changing resolution

Compress the video resolution to 144p:

ffmpeg -i input.mp4 -vf "scale=-1:144" -c:a copy -b:a 16k output.mp4

Crop the video

ffmpeg -i input.mp4 -vf "crop=w:h:x:y" output.mp4

Cut the video

ffmpeg -ss 00:00:00.00 -i input.mp4 -t 00:00:00.00 -c copy output.mp4

-ss: Starting point
-to: Ending point
-t: Duration

Concatenating videos

ffmpeg -f concat -safe 0 -i input1.mp4 -i input2.mp4 -c copy output.mp4

Adding thumbnails

ffmpeg -loop 1 -i cover.jpg -i input.mp4 -c:v libx264 -c:a copy output.mp4

Rotating the video

ffmpeg -i input.mp4 -vf "transpose=2" output.mp4

1 = 90 degrees clockwise
2 = 90 degrees counter-clockwise

Speeding the video

# 2× speed:
ffmpeg -i input.mp4 -filter_complex "[0:v]setpts=0.5*PTS;[0:a]atempo=2.0[a]" -map "[v]" -map "[a]" output.mp4

# 8× speed:
ffmpeg -i input.mp4 -filter_complex "[0:v]setpts=0.125*PTS[v];[0:a]atempo=8.0[a]" -map "[v]" -map "[a]" output.mp4

# Speeding and scaling at the same time:
ffmpeg -i input.mp4 -filter_complex "[0:v]setpts=0.125*PTS[v],scale=-1:144;[0:a]atempo=8.0[a]" -map "[v]" -map "[a]" output.mp4

Convert to an animated image

Convert to animated WebP image:

ffmpeg -i input.mp4 -vf "scale=360:-1,fps=12" -c:v libwebp_anim -loop 0 -compression_level 6 -quality 70 -an output.webp

Adding watermarks

ffmpeg -i input.mp4 -i watermark.png -filter_complex "[0:v][1:v]overlay=10:10:enable='between(t,1,2)'[outv]" -map "[outv]" output.mp4