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
 
   # -----