Encode mp4, webm and gif using ffmpeg (2.6 or above). Audio is discarded on all of these!

gifenc.sh

#!/bin/sh

# sh gifenc.sh input.mp4 output.gif
# Optionally accepts width / height (one or both).

palette="/tmp/palette.png"
filters="fps=15"
if [ -n "$3" ]; then
  if [ -n "$4" ]; then
    filters="$filters,scale=$3:$4"
  else
    filters="$filters,scale=$3:-1"
  fi
  filters="$filters:flags=lanczos"
fi

ffmpeg -v warning -i "$1" -vf "$filters,palettegen" -y $palette
ffmpeg -v warning -i "$1" -i $palette -lavfi "$filters [x]; [x][1:v] paletteuse" -y "$2"

mp4enc.sh

#!/bin/sh

# sh mp4enc.sh input.mp4 output.mp4 [quality]
# Optionally accepts a "quality" parameter (defaults to 640).
# https://www.virag.si/2012/01/web-video-encoding-tutorial-with-ffmpeg-0-9

quality="640k"
if [ -n "$3" ]; then
  quality="$3k"
fi
options="-c:v libx264 -b:v $quality -maxrate $quality -bufsize 1000k -profile:v high -preset veryslow -tune film -movflags +faststart -threads 1"

ffmpeg -y -i "$1" $options -pass 1 -an -f rawvideo /dev/null && ffmpeg -i "$1" $options -pass 2 -an "$2"

webmenc.sh

#!/bin/sh

# sh wemenc.sh input.mp4 output.webm [quality]
# Optionally accepts a "quality" parameter (defaults to 700).
# https://www.virag.si/2012/01/webm-web-video-encoding-tutorial-with-ffmpeg-0-9

quality="700k"
if [ -n "$3" ]; then
  quality="$3k"
fi
options="-c:v libvpx -b:v $quality -maxrate $quality -bufsize 1000k -preset veryslow -tune film -movflags +faststart -threads 1"

ffmpeg -y -i "$1" $options -pass 1 -an -f rawvideo /dev/null && ffmpeg -i "$1" $options -pass 2 -an "$2"

@Zettt Apologies for the multi-year delay here, I missed your comments before! I've applied your suggestion, we certainly don't want word splitting.