DAR to VAR, bash

7. 9. 2022

Shocking facts: 1440x1080 and 1920x1080 videos may both be marked with DAR=16:9. To get the DAR from input video for purposes of calculating output resizing with ‘square’ pixels:

With ffprobe

file="20220721.mxf"
ffprobe="$(ffprobe -i $file 2>&1 | grep DAR | head -1)"
echo "ffprobe $ffprobe"

DAR="${ffprobe#*DAR }"
DAR="${DAR%]*}"
DAR="${DAR#* }"
echo; echo "$DAR"

DAR="${DAR//://}"
DAR="$(bc -l <<< "$DAR")"
echo "$DAR"

With mediainfo

file="20220721.mxf"
DAR="$(mediainfo --Inform="Video;%DisplayAspectRatio%" "$file")"
echo "$DAR" 

If DAR comes out as 1.7777 (16:9), and my new wanted width is 1000px, then height would be

height = width / DAR
height = 1000 / 1.7777
height = 562.5 = 563 px
# or perhaps round to nearest even number, so 562

Rounding to nearest even number, some bc and awk (returns ‘correct’ results)

awk_round () {
    awk 'BEGIN{printf "%."'$1'"f\n", "'$2'"}'
}
even () {
    local numr tmp
    numr="$1"
    tmp="$(echo "($numr) / 2" | bc -l)"
    tmp="$(awk_round 0 "$tmp")"
    tmp="$(( tmp * 2 ))"
    echo "$tmp"
}

even "562.5"
562
even "562.6"
562
even "562.9"
562
even "563"
564
even "563.3"
564
even "563.9"
564

bash video mine