jblooper.sh

#!/bin/bash

# Tested with ffmpeg 2.8.4

if [ -z "$1" ] || [ -z "$2" ] || [ -z "$3" ]; then
    echo "Please provide audio file, video file and output file"
    echo "For example: audio.mp3 video.mp4 output.mp4"
    exit
fi

audio=$(realpath -q $1)
video=$(realpath -q $2)
output=$(realpath -q $3)

if [ -z "$audio" ]; then
    echo "Couldn't find audio file ${1}"
    exit
fi

if [ -z "$video" ]; then
    echo "Couldn't find audio file ${2}"
    exit
fi

# Get audio & video lengths
audio_duration=$(ffprobe -i ${audio} -show_entries format=duration -v quiet -of csv="p=0")
video_duration=$(ffprobe -i ${video} -show_entries format=duration -v quiet -of csv="p=0")

# Check to how many audio loops should be done
if [ $(echo " $audio_duration > $video_duration" | bc) -eq 1 ]; then
    # Audio is longer
    n_loops=$(echo "(${audio_duration} / ${video_duration}) + 1"|bc)
else
    # Video is shorter or equal to audio, just do one loop
    n_loops=1
fi

ffmpeg -i ${audio} -f concat -i <(for i in $(seq 1 ${n_loops}); do printf "file '%s'\n" ${video}; done) -c:v copy -c:a copy -shortest ${output}