fade_out_fade_in.sh

#!/bin/sh

set -eu

input=$1
output=$2
time=$3

fade_out_duration=0.5
fade_in_duration=0.5
fade_out_offset=0.5
fade_in_offset=0.5
afade_out_duration=0.5
afade_in_duration=0.5
afade_out_offset=0
afade_in_offset=0

fade_out_start_time=$(
  echo "${time} - ${fade_out_duration} - ${fade_out_offset}" | bc
)
fade_in_start_time=${fade_in_offset}
afade_out_start_time=$(
  echo "${time} - ${afade_out_duration} - ${afade_out_offset}" | bc
)
afade_in_start_time=${afade_in_offset}

filter_graph="\
[0:v] split=2 [vcopy1][vcopy2]; \
[vcopy1] trim=end=${time},setpts=PTS-STARTPTS [vpart1], \
[vcopy2] trim=start=${time},setpts=PTS-STARTPTS [vpart2], \
[vpart1] fade=t=out:st=${fade_out_start_time}:d=${fade_out_duration} [vout1], \
[vpart2] fade=t=in:st=${fade_in_start_time}:d=${fade_in_duration} [vout2]; \
[vout1][vout2] concat=n=2:v=1:a=0 [vout]; \
[0:a] asplit=2 [acopy1][acopy2]; \
[acopy1] atrim=end=${time},asetpts=PTS-STARTPTS [apart1], \
[acopy2] atrim=start=${time},asetpts=PTS-STARTPTS [apart2], \
[apart1] afade=t=out:st=${afade_out_start_time}:d=${afade_out_duration} [aout1], \
[apart2] afade=t=in:st=${afade_in_start_time}:d=${afade_in_duration} [aout2]; \
[aout1][aout2] concat=n=2:v=0:a=1 [aout]\
"

ffmpeg \
  -threads 0 \
  -loglevel warning \
  -stats \
  -y \
  -i "${input}" \
  -vsync passthrough \
  -filter_complex "${filter_graph}" \
  -map "[vout]" \
  -map "[aout]" \
  "${output}"