[mediaplayer] use playerctl's formatting support

Ignores artist if absent (the hack of giving a control character default
and stripping it is unfortunately necessary at the moment, cf
altdesktop/playerctl#296)

Closes: vivien#498

mediaplayer/mediaplayer

@@ -52,17 +52,12 @@ if ($ENV{'BLOCK_BUTTON'} == 1) {
     system("playerctl $player_arg volume 0.01-");
 }
 
-my $artist = qx(playerctl $player_arg metadata artist 2>/dev/null);
-chomp $artist;
+my $metadata = qx(playerctl $player_arg metadata \\
+        --format '{{default(artist, "\004\005")}} - {{title}}' 2>/dev/null);
+chomp $metadata;
+$metadata =~ s/^\004\005 - //;
 # exit status will be nonzero when playerctl cannot find your player
-exit(0) if $? || $artist eq '(null)';
+exit(0) if $? || $metadata eq '(null)';
 
-push(@metadata, $artist) if $artist;
-
-my $title = qx(playerctl $player_arg metadata title);
-exit(0) if $? || $title eq '(null)';
-
-push(@metadata, $title) if $title;
-
-print(join(" - ", @metadata)) if @metadata;
+print($metadata) if $metadata;
 print("\n");