xfade

#!/bin/sh

# ffmpeg xfade transitions

# script usage
usage()
{
# if argument passed to function echo it
[ -z "${1}" ] || echo "! ${1}"
# display help
echo "\
# ffmpeg xfade transitions

$(basename "$0") -a clip1.(mp4|mkv|mov|m4v) -b clip2.(mp4|mkv|mov|m4v) -d duration -t transition -f offset -o outfile.mp4
-a clip1.(mp4|mkv|mov|m4v) : first clip
-b clip2.(mp4|mkv|mov|m4v) : second clip
-d duration                : transition duration
-t transition              : transition
-f offset                  : offset
-o outfile.mp4             : optional agument # if option not provided defaults to infile-name-xfade-date-time

+ transitions

circleclose, circlecrop, circleopen, diagbl, diagbr, diagtl, diagtr, dissolve, distance
fade, fadeblack, fadegrays, fadewhite, hblur, hlslice, horzclose, horzopen, hrslice
pixelize, radial, rectcrop, slidedown, slideleft, slideright, slideup, smoothdown
smoothleft, smoothright, smoothup, squeezeh, squeezev, vdslice, vertclose, vertopen, vuslice
wipebl, wipebr, wipedown, wipeleft, wiperight, wipetl, wipetr, wipeup"
exit 2
}

# error messages
NOTFILE_ERR='not a file'
INVALID_OPT_ERR='Invalid option:'
REQ_ARG_ERR='requires an argument'
WRONG_ARGS_ERR='wrong number of arguments passed to script'

# if script is run arguments pass and check the options with getopts,
# else display script usage and exit
[ $# -gt 0 ] || usage "${WRONG_ARGS_ERR}"

# getopts check and validate options
while getopts ':a:b:d:t:f:o:h' opt
do
  case ${opt} in
     a) clip1="${OPTARG}"
        [ -f "${clip1}" ] || usage "${clip1} ${NOTFILE_ERR}";;
     b) clip2="${OPTARG}"
        [ -f "${clip2}" ] || usage "${clip2} ${NOTFILE_ERR}";;
     d) dur="${OPTARG}";;
     t) transition="${OPTARG}";;
     f) offset="${OPTARG}";;
     o) outfile="${OPTARG}";;
     h) usage;;
     \?) usage "${INVALID_OPT_ERR} ${OPTARG}" 1>&2;;
     :) usage "${INVALID_OPT_ERR} ${OPTARG} ${REQ_ARG_ERR}" 1>&2;;
  esac
done
shift $((OPTIND-1))

# infile, infile name and extension
clip1_nopath="${clip1##*/}"
clip1_name="${clip1_nopath%.*}"

# defaults
duration_default='0.5'
transition_default='fade'
outfile_default="${clip1_name}-xfade-$(date +"%Y-%m-%d-%H-%M-%S").mp4"

# offset and duration options not set
if [ -z "${offset}" ];then
    # clip 1 duration to calculate default transition offset
    clip1_dur=$(ffprobe -v error -show_entries format=duration -of default=noprint_wrappers=1:nokey=1 "${clip1}")
    
    # round down decinal point
    clip1_time=$(printf "%.1f\n" "${clip1_dur}")
    
    # clip1 duration minus duration default and 0.1 seconds which is needed for the transition
    offset_default=$(echo "${clip1_time}" - "${dur:=${duration_default}}" - 0.1 | bc -l)
    
    # audio trim default match offset default
    audio_trim_default=$(echo "${clip1_time}" - 0.1 | bc -l)
else
    # offset and duration options set
    # trim audio to match length of the duration and offset
    audio_trim=$(echo "${dur} + ${offset}" | bc -l)
fi

# cross fade video and audio
xfade_va () {
    ffmpeg \
    -hide_banner \
    -stats -v panic \
    -i "${clip1}" -i "${clip2}" \
    -filter_complex \
    "[0:v][1:v]xfade=transition='${transition:=${transition_default}}':duration='${dur:=${duration_default}}':offset='${offset:=${offset_default}}'[xfade];
    [0:a]atrim=0:'${audio_trim:=${audio_trim_default}}'[atrim];
    [atrim][1:a]acrossfade=d='${dur:=${duration_default}}'[afade]
    " \
    -map "[xfade]" -map "[afade]" \
    -pix_fmt yuv420p \
    -movflags +faststart -f mp4 \
    "${outfile:=${outfile_default}}"
}


# run the xfade_va function
xfade_va "${clip1}" "${clip2}"