webm conversion for spark preview videos

spark-webm.sh

#!/bin/bash

# https://trac.ffmpeg.org/wiki/Encode/VP9
# Converts video file to webm using two-pass encoding
# Installation on Mac: add script to /usr/local/bin
# Usage: 
#   webm ./path/to/video.mp4
#   Outputs ./path/to/video.mp4.webm

# Max size is 720 pixels wide. Change -vf scale to adjust
# Set -crf to lower number for higher quality, longer encode time, and larger files. https://developers.google.com/media/vp9/settings/vod#quality
# -an strips audio, -c:a libopus copies audio

ffmpeg -i $1 -vf scale=720:-1 -c:v libvpx-vp9 -b:v 0 -crf 32 -pass 1 -an -f null /dev/null
ffmpeg -i $1 -vf scale=720:-1 -c:v libvpx-vp9 -b:v 0 -crf 32 -pass 2 -an $1.webm