Media Lovin' Toolkit (MLT) is an open source multimedia framework, designed and developed for television broadcasting. It provides a toolkit for broadcasters, video editors, media players, transcoders, web streamers and many more types of applications.
MLT is written in C.
The functionality of the system is provided via an assortment of ready to use tools, XML authoring components, and an extensible plug-in based API - wikipedia 
It is used by video editors Kdenlive, OpenShot and Shotcut among others.
# Functionality
Comprehensive and optimized suite of video and audio effects including: - image scaling - alpha-compositing - deinterlacing - masking - motion-tracking - audio mixing - audio gain, and wipe transitions
Integration with many libraries for multimedia including: - FFmpeg - WebVfx - LADSPA audio plugins - SoX audio effects - JACK audio routing - frei0r video plugins - An XML authoring schema - YAML-based metadata - Live IP streaming output via FFmpeg
- Language bindings for C++, C#, Java, Lua, Perl, PHP, Python, Ruby, and TCL - Cross-platform: Linux, BSD, Mac OS X, Windows (MinGW)
# See also - MLT Multimedia Framework * Technical overview