Common switches

-codecs    # list codecs
-c:v       # video codec (-vcodec) - 'copy' to copy stream
-c:a       # audio codec (-acodec)

-fs SIZE         # limit file size (bytes)

-b:v 1M          # video bitrate (1M = 1Mbit/s)
-b:a 1M          # audio bitrate

-aspect RATIO    # aspect ratio (4:3, 16:9, or 1.25)
-r RATE          # frame rate per sec
-s WIDTHxHEIGHT  # frame size
-vn              # no video

-aq QUALITY      # audio quality (codec-specific)
-ar 44100        # audio sample rate (hz)
-ac 1            # audio channels (1=mono, 2=stereo)
-an              # no audio
-vol N           # volume (256=normal)

-acodec
-vcodec

Ringtone conversion using ffmpeg

ffmpeg -i foo.mp3 -ac 1 -ab 128000 -f mp4 -acodec libfaac -y target.m4r

To web

# no audio
ffmpeg -i input.mov -vcodec h264   -an -strict -2 output.mp4
ffmpeg -i input.mov -vcodec libvpx -an output.webm

ffmpeg -i input.mov -vcodec h264 -acodec aac -strict -2 output.mp4
ffmpeg -i input.mov -vcodec libvpx -acodec libvorbis output.webm

<video width="320" height="240" controls>
  <source src="movie.mp4" type='video/mp4'></source>
  <source src="movie.webm" type='video/ogg'></source>
</video>