generate story book from a list of audio and image files

generate-story-book.sh

#!/bin/zsh
# Usage: generate-story-book <output> <audio_files_pattern> <image_files_pattern>

emulate -LR zsh
set -e

output=$1
audio_files_pattern=$2
image_files_pattern=$3

SILENCE_DURATION=2
FFMPEG_FLAGS=(-v error -y)

make-silence() {
    local duration=$1
    local output=silence.mp3
    ffmpeg $FFMPEG_FLAGS -f lavfi -i "anullsrc=r=44100:cl=mono" -t $duration -q:a 9 -acodec libmp3lame ${output}
    echo $output
}

concat-audio() {
    # concat-audio <output> <audio files>
    local output=$1
    shift
    ffmpeg $FFMPEG_FLAGS -i "concat:${(j:|:)@[1,-1]}" -acodec copy $output
}

convert-to-mp3() {
    reply=()
    echo -n "Converting aif to mp3\t"
    for aif_file in $*; do
        mp3_file=$(basename $aif_file .aif).mp3
        ffmpeg $FFMPEG_FLAGS -i $aif_file -f mp3 -acodec libmp3lame -ab 192000 -ar 44100 $mp3_file
        echo -n .
        reply+=($mp3_file)
    done
    echo done
}

pad-audio-files() {
    echo -n "Padding audio files\t"
    silence=$(make-silence $SILENCE_DURATION)
    reply=()
    for audio_file in $*; do
        padded=$(basename $audio_file .mp3)-padded.mp3
        concat-audio $padded $silence $audio_file $silence
        echo -n .
        reply+=($padded)
    done
    rm $silence
    echo done
}

make-pages() {
    reply=()
    echo -n "Making story book pages\t"
    for audio_file image_file in $*; do
        page=$(basename $audio_file .mp3).mp4
        ffmpeg $FFMPEG_FLAGS -loop 1 -i $image_file -i $audio_file -acodec copy -shortest $page
        echo -n .
        reply+=($page)
        rm $audio_file
    done
    echo done
}

convert-to-mp3 ${~audio_files_pattern}
mp3_audio_files=($reply)
pad-audio-files $mp3_audio_files
padded_audio_files=($reply)

image_files=(${~image_files_pattern})
make-pages ${padded_audio_files:^image_files}
pages=($reply)

echo "Calculating transitions"
ffmpeg-concat -t BookFlip -d 1000 $pages

echo -n "Converting audio to AAC..."
ffmpeg $FFMPEG_FLAGS -i out.mp4 -c:v copy -c:a aac $output
echo done

rm $pages

echo "Output file is $output"