h264 transcode using ffmpeg/vaapi for older hardware

vaapi_ffmpeg_transcode.sh

#!/usr/bin/env bash
# Description: Convert all mkv files in a directory to mp4 using ffmpeg and vaapi

# set -x

convert_file() {
  input_filename="$1"
  output_filename="${input_filename%.mkv}.mp4"

  python3 -c 'header=" BEGIN converting '"$input_filename "'"; print(f"{header:*^80}")'

  # I was running this in a jellyfin LXC with GPU passthrough, you may need to change the path to the ffmpeg binary
  /usr/lib/jellyfin-ffmpeg/ffmpeg \
    -hide_banner \
    -loglevel quiet \
    -stats \
    -hwaccel vaapi \
    -hwaccel_device /dev/dri/renderD128 \
    -hwaccel_output_format vaapi \
    -i "$input_filename" \
    -c:v h264_vaapi \
    -b:v 4M \
    -maxrate 8.5M \
    -bufsize 8.5M \
    -ac 2 \
    -c:a libfdk_aac \
    -vbr 3 "$output_filename"

  # XXX: This is a hack to get around the fact that I can't get the above command to work as a script
  # For some reason ffmpeg prints out a ton of stuff if I try to run as a script (looks like a memory dump), but it works find when I print the commands and run them manually
  # Really not sure why this is happening, but I'm not going to spend any more time on it
  #  cmd="/usr/lib/jellyfin-ffmpeg/ffmpeg -hide_banner -loglevel quiet -stats -hwaccel vaapi -hwaccel_device /dev/dri/renderD128 -hwaccel_output_format vaapi -i \"$input_filename\" -c:v h264_vaapi -b:v 4M -maxrate 8.5M -bufsize 8.5M -ac 2 -c:a libfdk_aac -vbr 3 \"$output_filename\""
  #  echo "$cmd"
}


# You can edit this find command to match your needs and filter out stuff if needed
find . -type f -iname '*.mkv' | while read line; do
  start_time=$(date +%s.%N)

  convert_file "$line"

  end_time=$(date +%s.%N)
  duration=$(echo "scale=3; ${end_time} - ${start_time}" | bc)

  echo "Finished converting $line in $duration seconds"
done

# set +x