+1 for tldr. For example, here's the output of `tldr ffmpeg`:

  ffmpeg

  Video conversion tool.
  See also: `gst-launch-1.0`.
  More information: https://ffmpeg.org/ffmpeg.html#Options.

  - Extract the sound from a video and save it as MP3:
    ffmpeg -i path/to/video.mp4 -vn path/to/sound.mp3

  - Transcode a FLAC file to Red Book CD format (44100kHz, 16bit):
    ffmpeg -i path/to/input_audio.flac -ar 44100 -sample_fmt s16 path/to/output_audio.wav

  - Save a video as GIF, scaling the height to 1000px and setting framerate to 15:
    ffmpeg -i path/to/video.mp4 -filter:v 'scale=-1:1000' -r 15 path/to/output.gif

  - Combine numbered images (frame_1.jpg, frame_2.jpg, etc) into a video or GIF:
    ffmpeg -i path/to/frame_%d.jpg -f image2 video.mpg|video.gif

  - Trim a video from a given start time mm:ss to an end time mm2:ss2 (omit the -to flag to trim till the end):
    ffmpeg -i path/to/input_video.mp4 -ss mm:ss -to mm2:ss2 -codec copy path/to/output_video.mp4

  - Convert AVI video to MP4. AAC Audio @ 128kbit, h264 Video @ CRF 23:
    ffmpeg -i path/to/input_video.avi -codec:a aac -b:a 128k -codec:v libx264 -crf 23 path/to/output_video.mp4

  - Remux MKV video to MP4 without re-encoding audio or video streams:
    ffmpeg -i path/to/input_video.mkv -codec copy path/to/output_video.mp4

  - Convert MP4 video to VP9 codec. For the best quality, use a CRF value (recommended range 15-35) and -b:v MUST be 0:
    ffmpeg -i path/to/input_video.mp4 -codec:v libvpx-vp9 -crf 30 -b:v 0 -codec:a libopus -vbr on -threads number_of_threads path/to/output_video.webm