Concat mp4 files with ffmpeg

concat_mp4.sh

#!/bin/bash

#ffmpeg -f concat -i <(find . -name '*.mp4' -printf "file '%p'\n") -c copy output.mp4
#ffmpeg -f concat -i <(printf "file '$(pwd)/%s'\n" *.mp4)  -c copy output.mp4
#ffmpeg -f concat -i <(for f in ./*.mp4; do echo "file '$f'"; done) -c copy output.mp4

list_file="list.txt"
archive_path="processed"

function get_unique_dates {
    pattern="20*.mp4"
    (for file in $pattern; do 
        date=${file:0:8}
        hour=${file:9:2}

        printf '%s_%s\n' $date $hour
    done) | uniq
}

function generate_file_list {
    list_file=$1
    datehour=$2  # e.g., 20170905_17
    suffix=$3  # F: front, R: rear

    (for file in $(find . -name "${datehour}*${suffix}.mp4"); do
        echo "file $file";
    done) > $list_file
}

function concat_media_files {
    list_file=$1
    output_file=$2
    datehour=$3

    date=${datehour:0:6}
    hour=${datehour:7:2}

    ffmpeg -f concat -safe 0 -i $list_file \
        -metadata ICRD="$date $hour:00:00" \
        -map_metadata 0:g \
        -c copy "$output_file" -y

    # NOTE: It seems ffmpeg does not actually map the metadata properly,
    # so we are overriding the file modification date
    if [[ -f $output_file ]]; then
        touch -t $(printf '%s%s00' $date $hour) "$output_file"
    fi
}

function archive_processed_files {
    list_file=$1
    archive_path=$2

    while read line; do
        set $line
        mv $2 $archive_path/
    done < $list_file
}

mkdir $archive_path

for datehour in $(get_unique_dates); do
    generate_file_list "$list_file" $datehour "F"
    output="Dashboard Cam Front $datehour.mp4"
    concat_media_files "$list_file" "$output" $datehour
    archive_processed_files "$list_file" "$archive_path"

    generate_file_list "$list_file" $datehour "R"
    output="Dashboard Cam Rear $datehour.mp4"
    concat_media_files "$list_file" "$output" $datehour
    archive_processed_files "$list_file" "$archive_path"
done

ffmpeg -f concat -safe 0 -i <(for f in *R.MP4; do echo "file `pwd`/'$f'"; done) -c copy Rear.mp4