Multichannel News writes that Discovery Communications will switch the HD compression format of Discovery, TLC, Animal Planet, Science and Planet Green channels from MPEG-2 to MPEG-4 format, therefore freeing up more satellite transponder space. MPEG-4 is a more efficient video compression scheme and descendant of MPEG-2 which is still heavily used in broadcast (and on DVDs). So far, Animal Planet and Science networks have been converted to the MPEG-4 HD format. In September, Discovery, TLD and Planet Green will be converted to MPEG-4. To learn more about MPEG-4 try this Wikipedia page.
Source: Multichannel News