feat: Use ffmpeg for cover art on non mpeg-4 containers instead of mp4art from deprecated mp4v2-utils package

Closes: https://github.com/KrumpetPirate/AAXtoMP3/issues/203

AAXtoMP3

@@ -968,7 +968,29 @@ do
 
   if [ -f "${cover_file}" ]; then
     log "Adding cover art"
+    # FFMGEP does not support MPEG-4 containers fully #
+    if [ "${container}" == "mp4" ] ; then
       mp4art --add "${cover_file}" "${output_file}"
+    # FFMPEG for everything else #
+    else
+      # 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}"
+    fi
   fi
 
   # -----

README.md

@@ -220,13 +220,17 @@ brew install findutils
 ```
 
 #### mp4art/mp4chaps
-_Note: This is an optional dependency._
+_Note: This is an optional dependency, required for adding cover art to m4a and b4b files only._
 
 __Ubuntu, Linux Mint, Debian__
 ```
 sudo apt-get update
 sudo apt-get install mp4v2-utils
 ```
+
+On Debian and Ubuntu the mp4v2-utils package has been deprecated and removed, as the upsteam project is no longer maintained.
+The package was removed in Debian Buster, and Ubuntu Focal [ 20.04 ].
+
 __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.