#!/bin/sh

input_video=$1
input_audio=$2

if [[ -z "$1" ]] || [[ -z "$2" ]]
then
	echo Invalid input
	echo "\"$0 <input video> <input audio>\""
	exit 1
fi

tmp_video=tmp$$.mp4

function get_duration() {
	ffmpeg -i $1 2>&1 | \
		awk -F, '/Duration/{print $1}' | \
		awk -F: '{print $2*3600 + $3*60 + $4}'
}

duration_audio=`get_duration $input_audio`
echo Duration of audio is $duration_audio seconds

duration_video=`get_duration $input_video`
echo Duration of video is $duration_video seconds

av_ratio=$(echo "2k $duration_audio $duration_video / p" | dc)
echo Calculated audio/video ratio is $av_ratio


# make video about the same length as the audio
ffmpeg \
	-i $input_video \
	-filter:v "setpts=${av_ratio}*PTS" \
	$tmp_video

# adds audio to video,
# compresses audio
ffmpeg \
	-i $tmp_video \
	-i $input_audio \
	-c:v copy \
	-map 0:v:0 \
	-map 1:a:0 \
	-c:a aac \
	-b:a 192k \
	output.mp4

[[ -f $tmp_video ]] && rm $tmp_video