Bash script to transcode video and audio clips to Davinci Resolve accepted codec.

resolve-transcode.sh

#!/bin/bash
#-------------------------------------------------------------------------------------
# Convert all clips in a directory to Davinci Resolve compatible format.
# Will work on both audio and video files.
# Creates two subdirectories in current directory:
# - ORIGINAL (where the input files will be moved after conversion) 
# - TRANSCODED (where the converted files will be created)
#
# Originally I used as output format prores which made the script much
# simpler but the output files were massive. I then switched to DNxHD/DNxHR format
# which is far more finnicky as the files need to be encoded with specific bitrates
# according to the frameratem but the advantage is in having smaller files.
# Another format which I also tried is simple mpeg4 which is as easy to use as prores
# and the resulting size is very small, but the downside is the degraded quality.
# I haven't done any rigorous testing on this, so feel free to change or modify
# the script below and let me know.
# 
# Notes:
# - needs ffmpeg and exiftool available in path;
# - exiftool is used at end of the conversion to copy the "CreateDate" tag
#   to "FileModifyDate" tag otherwise Resolve doesn't pick up the correct
#   creation date (I use the sort on creation date to put order in the media view).
# - see table at the end of the script for information on the DNxHD format and 
#   accepted framerate;
# - the low-disk-usage codec can be activated by replacing all the if-then blocks
#   and simply put "-vcodec mpeg4" in the ffmpeg options; maybe an option can be
#   added to allow the user to switch to this codec if quality preservation is not
#   paramount (maybe some further tests are needed).
#-------------------------------------------------------------------------------------

counter=0
ORIGINAL_DIR="ORIGINAL"
TRANSCODED_DIR="TRANSCODED"

if [ ! -d "$ORIGINAL_DIR" ]; then
    mkdir $ORIGINAL_DIR
fi

if [ ! -d "$TRANSCODED_DIR" ]; then
    mkdir $TRANSCODED_DIR
fi

current_time=$(date +"%Y/%m/%d %H:%M:%S")
echo "---> START $current_time (working directory: $PWD)" 

videotypes=("m4v" "mp4" "mov")
audiotypes=("flac" "mp3" "aac" "wma" "ogg" "oga" "mogg" "raw")

OIFS="$IFS"
for extaudio in "${audiotypes[@]}"; do
    IFS=$'\n'
    for file in `find . -maxdepth 1 -type f -iname "*.${extaudio}" -exec basename {} \;`; do
        counter=$[$counter +1]
        echo "---> [$counter] $file TRANSCODING TO ${file%.*}-PCM.wav"
        IFS="$OIFS"
        ffmpeg -i "$file" -hide_banner -acodec pcm_s16le "$TRANSCODED_DIR/${file%.*}-PCM.wav"
        IFS=$'\n'
        mv "$file" -t $ORIGINAL_DIR
        done
done
IFS="$OIFS"

OIFS="$IFS"
for ext in "${videotypes[@]}"; do
    IFS=$'\n'
    for file in `find . -maxdepth 1 -type f -iname "*.${ext}" -exec basename {} \;`; do
        counter=$[$counter +1]

        size=$(exiftool -v0 -short3 -imagesize $file)
        framerate=$(exiftool -v0 -short3 -videoframerate $file)
        bitrate=$(exiftool -v0 -short3 -avgbitrate $file)
        codec=$(exiftool -v0 -short3 -compressorname $file)

        if [[ $size == "3840x2160" ]]; then
            suffix='-DNxHR'
            echo ".....transcoding input 4K file to DNxHR codec with profile HQ"
            options='-hide_banner -map_metadata 0 -vcodec dnxhd -profile:v dnxhr_hq -acodec pcm_s16le -pix_fmt yuv422p'
        elif [[ $size == "1920x1080" ]]; then
            suffix='-DNxHD'
            if [[ ${framerate} == "23.967" ]]; then
            
                echo ".....transcoding HD to DNxHD bitrate 36M, fps=23.967"
                options='-hide_banner -map_metadata 0 -vcodec dnxhd -b:v 36M -acodec pcm_s16le -r 24000/1001 -pix_fmt yuv422p'
            elif [[ ${framerate} == "25" ]]; then
                echo ".....transcoding HD to DNxHD bitrate 36M, fps=25"
                options='-hide_banner -map_metadata 0 -vcodec dnxhd -b:v 36M -acodec pcm_s16le -pix_fmt yuv422p'
            elif [[ ${framerate} == "29.97" ]]; then
                echo ".....transcoding HD to DNxHD bitrate 45M, fps=29.97"
                options='-hide_banner -map_metadata 0 -vcodec dnxhd -b:v 45M -acodec pcm_s16le -r 30000/1001 -pix_fmt yuv422p'
            elif [[ ${framerate} == "50" ]]; then
                echo ".....transcoding HD to DNxHD bitrate 75M, fps=50"
                options='-hide_banner -map_metadata 0 -vcodec dnxhd -b:v 75M -acodec pcm_s16le -r 60000/1001 -pix_fmt yuv422p'
            elif [[ ${framerate} == "59.94" ]]; then
                echo ".....transcoding HD to DNxHD bitrate 90M, fps=59.94"
                options='-hide_banner -map_metadata 0 -vcodec dnxhd -b:v 90M -acodec pcm_s16le -r 60000/1001 -pix_fmt yuv422p'
            else
                echo ".....input fps is not standard (23.967, 25, 29.97, 50, 59.94), aborting."
                exit
            fi
        fi
        IFS="$OIFS"

        echo "---> [$counter] input:$file output:${file%.*}$suffix.mov"
        echo "---> [$counter] resolution: $size, fps: $framerate, bitrate: $bitrate, codec: $codec"
        ffmpeg -i $file ${options} "$TRANSCODED_DIR/${file%.*}$suffix.mov"
        # following command copies CreateDate tag to FileModifyDate because it seems Resolve looks
        # at this tag as the equivalent for creation date
        exiftool "-FileModifyDate<CreateDate" -overwrite_original -progress "$TRANSCODED_DIR/${file%.*}$suffix.mov"
        IFS=$'\n'
        mv "$file" -t $ORIGINAL_DIR
    done
done
IFS="$OIFS"

current_time=$(date +"%Y/%m/%d %H:%M:%S")
echo "---> END $current_time"


#-------------------------------------------------------------------------------------
# DNxHD, DNxHR references:
#
# https://askubuntu.com/questions/907398/how-to-convert-a-video-with-ffmpeg-into-the-dnxhd-dnxhr-format
# http://avid.force.com/pkb/articles/en_US/White_Paper/DNxHR-Codec-Bandwidth-Specifications
#
# | Frame size | Bitrate | Pixel Format | FPS             |
# | ---------- | ------- | ------------ | ----------------|
# |*1920x1080p | 36Mbps  | yuv422p      | 24 (24000/1001) |
# | 1920x1080p | 115Mbps | yuv422p      | 24 (24000/1001) |
# | 1920x1080p | 175Mbps | yuv422p      | 24 (24000/1001) |
# |*1920x1080p | 36Mbps  | yuv422p      | 25              |
# | 1920x1080p | 120Mbps | yuv422p      | 25              |
# | 1920x1080p | 185Mbps | yuv422p      | 25              |
# | 1920x1080p | 45Mbps  | yuv422p      | 30 (30000/1001) |
# |*1920x1080p | 145Mbps | yuv422p      | 30 (30000/1001) |
# | 1920x1080p | 220Mbps | yuv422p      | 30 (30000/1001) |
# |*1920x1080p | 75Mbps  | yuv422p      | 50              |
# | 1920x1080p | 240Mbps | yuv422p      | 50              |
# | 1920x1080p | 365Mbps | yuv422p      | 50              |
# |*1920x1080p | 90Mbps  | yuv422p      | 60 (60000/1001) |
# | 1920x1080p | 290Mbps | yuv422p      | 60 (60000/1001) |
# | 1920x1080p | 440Mbps | yuv422p      | 60 (60000/1001) |