Install FFMPEG on OS X with HomeBrew to convert Mp4 to WebM

ffmpeg-install.sh

# Installation
brew install ffmpeg --with-vpx --with-vorbis --with-libvorbis --with-vpx --with-vorbis --with-theora --with-libogg --with-libvorbis --with-gpl --with-version3 --with-nonfree --with-postproc --with-libaacplus --with-libass --with-libcelt --with-libfaac --with-libfdk-aac --with-libfreetype --with-libmp3lame --with-libopencore-amrnb --with-libopencore-amrwb --with-libopenjpeg --with-openssl --with-libopus --with-libschroedinger --with-libspeex --with-libtheora --with-libvo-aacenc --with-libvorbis --with-libvpx --with-libx264 --with-libxvid

# Easy Peasy
ffmpeg -i video.mp4 video.webm

# FFMPEG convert video with multiple audio streams
# https://video.stackexchange.com/questions/12051/ffmpeg-convert-video-with-multiple-audio-streams
ffmpeg -i "The Bunker.avi" -map 0:0 -map 0:1 -map 0:2 -vcodec h264 -acodec:0 mp3 -acodec:1 mp3 TheBunkerNwMix.mp4