Gmerlin is a multimedia framework, which allows you to quickly
develop multimedia applications. It is built upon gavl (for low
level Audio/Video things) and libxml2 (for loading and saving
configuration data and other things). The gmerlin API can be used
at multiple levels: Either you take the basic things like plugins,
fifos, message-queues and gavl audio/video converters and build
your own media engine. The other possibility is to use the player
or transcoder engines directly. The latter approach is probably
easier, but you'll have less freedom in controlling the process.

Gmerlin includes GUI player with mediatree and a GUI transcoder
among other things.

WWW: http://gmerlin.sourceforge.net/