Add a gentle fade-in from black to the beginning and a matching fade-out to the end of a video clip

add-fades-to-video.sh

#!/bin/bash


destfile() {
    dir=$(dirname "$1")
    filename=$(basename -- "$1");
    extension="${filename##*.}";
    basename="${filename%.*}";
    filepath="${dir}/${basename}-faded.${extension}";
    c=0
    while [ -f "$filepath" ]; do
        c=$((c+1))
        filepath="${dir}/${basename}-faded-${c}.${extension}";
    done
    echo "${filepath}";
}


SRCFILE=$1
FADEIN=${2:-'1.5'}
FADEOUT=${3:-$FADEIN}

if [ "${SRCFILE}" == "" ]; then
    echo "You must provide a source file";
    exit;
fi

if [ ! -f "${SRCFILE}" ]; then
    echo "${SRCFILE} does not exists.";
    exit;
fi

echo "reading from ${SRCFILE}";
OUTFILE=$(destfile "${SRCFILE}");
echo "writing to ${OUTFILE}"

LENGTH=$(ffprobe -v error -show_entries format=duration -of default=noprint_wrappers=1:nokey=1 "${SRCFILE}")
STARTFADEOUT=$(echo "${LENGTH} ${FADEOUT}" | awk '{ print $1-$2 }')

ffmpeg -i "${SRCFILE}" -vf "fade=t=in:st=0:d=${FADEIN},fade=t=out:st=${STARTFADEOUT}:d=${FADEOUT}" "${OUTFILE}"

echo "done writing ${OUTFILE}."