Convert all MKV files in a folder to MP4

mkv_to_mp4.sh

#!/usr/bin/env bash

# 16:9 ratio suggestion
$max_width=768
$max_height=432

# 4:3
# $max_width=640
# $max_height=480

for file in *mkv; do

  # EXPLANATION OF FLAGS
  # -y                           Overwrites existing files by the same name without asking.
  # -i                           The input file.
  # -strict -2                   Lets ffmpeg use experimental codecs, which it won't by default.
  # -r                           Sets the frame rate of the output file.
  # -v scale=<width>:<height>    Sets the width/height of the output. Nested if statements make sure it only scales
  #                              the video DOWN to the desired size, not up.
  
  ffmpeg -y  \
  -i "$file" \
  -strict -2 \
  -r 30      \
  -vf "scale='if(gt(a,$max_width/$max_height),$max_width,-1)':'if(gt(a,$max_width/$max_height),-1,$max_height)'" \
  "$file.mp4"
done