#!/bin/sh

# create a side-by-side image or video from files made with the gopro hero3+ dual hero system sync cable.
# assumes that the two cameras were positioned unrotated side by side, which is unlike the default dual hero system configuration. this requires rotation of the left image.
# accepts left and right files in any order and assumes that the file names have the automatically assigned 3D_L and 3D_R prefixes.
# usage: path1 path2

# select left and right image
if echo "$1" | grep -i "3d_l"
then
  left="$2"
  right="$1"
elif echo "$2" | grep -i "3d_l"
then
  left="$1"
  right="$2"
else
  echo error: file names must begin with 3d prefix. $@
  exit 1
fi

output=$(basename "$left")
output="$(dirname "$left")/sbs.$output"
extension=$(printf "$left" | tail -c 3)

if test mp4 = $extension
then
  # use only "-filter_complex hstack" for merge without any rotation.
  ffmpeg -y -i "$left" -i "$right" -filter_complex "[1]transpose=1,transpose=1[a];[0][a]hstack" -c:v libx264 -crf 17 -preset slow -c:a copy "$output"
elif test jpg = $extension
then
  convert "$left" -rotate 180 "$right" -rotate 180 +append "$output"
else
  echo error: invalid filename extension
  exit 1
fi