Bash Script to convert HDR video files into SDR format. Decent CPU can re-encode around 3-4x faster than video length.

gistfile1.txt

#!/bin/bash

function convert {
        filename=$(echo "$1" | cut -f 1 -d '.')
        newFilename=${filename}_HD.mkv

        if [ -f "$newFilename" ]; then
            echo \* $newFilename already exists!
        else
                COLORS=$(ffprobe -show_streams -v error "$1" |egrep "^color_transfer|^color_space=|^color_primaries=" |head -3)
                for C in $COLORS; do
                        if [[ "$C" = "color_space="* ]]; then
                                COLORSPACE=${C##*=}
                        elif [[ "$C" = "color_transfer="* ]]; then
                                COLORTRANSFER=${C##*=}
                        elif [[ "$C" = "color_primaries="* ]]; then
                                COLORPRIMARIES=${C##*=}
                        fi
                done
                if [ "${COLORSPACE}" = "bt2020nc" ] && [ "${COLORTRANSFER}" = "smpte2084" ] && [ "${COLORPRIMARIES}" = "bt2020" ]; then

                        # this file is HDR, convert a duplicate down to SDR
                        echo $1 contains HDR video track, creating duplicate SDR video file ${filename}...


                        ffmpeg -vsync 0 -hide_banner -v quiet -stats -hwaccel cuda -init_hw_device opencl=ocl -filter_hw_device ocl -extra_hw_frames 3 -threads 16 -c:v hevc_cuvid -resize 1920x1080 -i "$1" -vf "format=p010,hwupload,tonemap_opencl=tonemap=mobius:param=0.01:desat=0:r=tv:p=bt709:t=bt709:m=bt709:format=nv12,hwdownload,format=nv12" -c:a copy -c:s copy -c:v libx264 -max_muxing_queue_size 9999 "${newFilename}"
                else
                        echo \* $1 already SDR file, no need to convert!
                fi
        fi
}

for f in "$@"
do
        echo "Processing $f..."
        convert $f
        echo
done

./hdr2sdr *.mkv

Will create new files with the same filename, but "_HD.mkv" on the end of the filename.