Revert "feat: Use ffmpeg to cover add instead of mp4art from deprecated mp4v2-utils package"

This reverts commit 72794b6785.

This broke cover art addition for MPEG-4 containers

AAXtoMP3

@@ -968,23 +968,7 @@ do
 
   if [ -f "${cover_file}" ]; then
     log "Adding cover art"
-    # Create temporary output file name - ensure extention matches previous appropriate output file to keep ffmpeg happy
-    cover_output_file="${output_file%.*}.cover.${output_file##*.}"
-    # Copy audio stream from current output, and video stream from cover file, setting appropriate metadata
-    </dev/null "$FFMPEG" -loglevel quiet \
-      -nostats \
-      -i "${output_file}" \
-      -i "${cover_file}" \
-      -map 0:a:0 \
-      -map 1:v:0 \
-      -acodec copy \
-      -vcodec copy \
-      -id3v2_version 3 \
-      -metadata:s:v title="Album cover" \
-      -metadata:s:v comment="Cover (front)" \
-      "${cover_output_file}"
-      # Replace original output file with version including cover
-      mv "${cover_output_file}" "${output_file}"
+    mp4art --add "${cover_file}" "${output_file}"
   fi
 
   # -----

README.md

@@ -20,6 +20,7 @@ Audible fails for some reason.
 * GNU sed - see above
 * GNU find - see above
 * jq - only if `--use-audible-cli-data` is set or if converting an .aaxc file
+* mp4art used to add cover art to m4a and m4b files. Optional
 * mediainfo used to add additional media tags like narrator. Optional
 
 ## Usage(s)
@@ -218,6 +219,24 @@ brew install grep
 brew install findutils
 ```
 
+#### mp4art/mp4chaps
+_Note: This is an optional dependency._
+
+__Ubuntu, Linux Mint, Debian__
+```
+sudo apt-get update
+sudo apt-get install mp4v2-utils
+```
+__CentOS, RHEL & Fedora__
+```
+# CentOS/RHEL and Fedora users make sure that you have enabled atrpms repository in system. Let’s begin installing FFmpeg as per your operating system.
+yum install mp4v2-utils
+```
+__MacOS__
+```
+brew install mp4v2
+```
+
 #### mediainfo
 _Note: This is an optional dependency._