Você pode usar o aptitude para verificar quais pacotes fornecem um site específico:
aptitude search '?origin(Unofficial Multimedia Packages)'
p 2mandvd - Video DVD creator
p 2mandvd:amd64 - Video DVD creator
p 2mandvd-data - Video DVD creator (data files)
p aac-enc - Fraunhofer FDK AAC Codec Library - fronten
p aac-enc:amd64 - Fraunhofer FDK AAC Codec Library - fronten
p aacgain - Lossless mp4 normalizer with statistical a
p aacgain:amd64 - Lossless mp4 normalizer with statistical a
p aacplusenc - High-Efficency AAC (AAC+) Encoder.
p aacplusenc:amd64 - High-Efficency AAC (AAC+) Encoder.
p aacskeys - Decrypt all required keys from an AACS pro
p aacskeys:amd64 - Decrypt all required keys from an AACS pro
p acroread - Adobe Acrobat Reader: Portable Document Fo
p acroread-data - data files for acroread
p acroread-debian-files - Debian specific parts of Adobe Acrobat Rea
p acroread-debian-files:amd64 - Debian specific parts of Adobe Acrobat Rea
p acroread-dictionary-en - English dictionary for for acroread
p acroread-escript - Adobe EScript Plug-In
p acroread-fonts-jpn - Japanese fonts for Adobe acrobat reader
Ou pior, você pode simplesmente analisar a lista de pacotes diretamente:
grep Package /var/lib/apt/lists/ftp.deb-multimedia.org_dists_jessie_main_binary-i386_Packages
Package: 2mandvd
Package: 2mandvd-data
Package: aac-enc
Package: aacgain
Package: aacplusenc
Package: aacskeys
Package: acroread-debian-files
Package: acroread-fonts-jpn
Package: advancemenu
Package: aften