Just for comparison, my 32bit shows all is well:
libavcodec56:
Installed: 6:11.3-1
Candidate: 6:11.3-1
Version table:
*** 6:11.3-1 0
500 http://http.debian.net/debian/ unstable/main i386 Packages
100 /var/lib/dpkg/status
libavcodec55:
Installed: (none)
Candidate: (none)
Version table: