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

closes: https://github.com/KrumpetPirate/AAXtoMP3/issues/198

AAXtoMP3

@@ -962,7 +962,23 @@ do
 
   if [ -f "${cover_file}" ]; then
     log "Adding cover art"
-    mp4art --add "${cover_file}" "${output_file}"
+    # Create temporary output file name - ensure extention matches previous appropriate output file to keep ffmpeg happy
+    cover_output_file="${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
 
   # -----