Multicast DNS uses UDP port 5353, instead of port 53 used by conventional unicast DNS.
Currently, EtherPeek 4.1 on Mac OS X does not know that UDP port 5353 uses DNS-format packets, so it doesn't decode them. Fortunately, this is easy to fix: Just open the file "Edit EtherPeek.app/Contents/decoders/IETF.dcd" using your favourite text editor, and search for the line that says:
TEQU 35 2 0 0 DNS;Duplicate this line, and in the new copy change "35" (0x35 is 53 decimal) to 14e9 (0x14e9 is 5353 decimal), as shown in green below:
TEQU 19 2 0 0 SMTP; TEQU 35 2 0 0 DNS; TEQU 14e9 2 0 0 DNS; TEQU 50 2 0 0 HTTP; TEQU 6d 2 0 0 POP;
Now re-launch EtherPeek and it will be able to decode Multicast DNS packets.