Hacker Guide/Core

Introduction

The core of VLC media player is the LibVLC, which provides an interface for applications to handle features such as playlist management, audio and video decoding and output, a thread system. All the LibVLC source files are located in the src/ directory and its subdirectories:

• config/: load the configuration from command line and configuration file, provides functions for the modules to read and write to configuration
• control/: functions to control the behaviour of LibVLC, like Play/Pause, volume management, fullscreen, log verbosity, etc.
• extras/: mostly platform-specific code
• modules/: module management
• network/: network interface (socket management, network errors, etc.)
• osd/: On Screen Display manipulation
• test/: LibVLC needs to be tested, and not only by users :)
• text/: charset stuff
• interface/: contains code for user interaction such as key presses and device ejection.
• playlist/: manages playlist interaction such as stop, play, next, or random playback.
• input/: opens an input module, reads packets, parses them and passes reconstituted elementary streams to the decoder(s).
• video_output/: initializes the video display, gets all pictures and subpictures (ie. subtitles) from the decoder(s), optionally converts them to another format (such as YUV to RGB), and displays them.
• audio_output/: initializes the audio mixer, ie. finds the right playing frequency, and then resamples audio frames received from the decoder(s).
• stream_output/: functions to stream audio and video to the network
• misc/: miscellaneous utilities used in other parts of libvlc, such as the thread system, the message queue, CPU detection, the object lookup system, or platform-specific code.

Modules

The idea behind LibVLC is "modularity". The core gives a framework to do the media processing, from input (files, network streams) to output (audio or video, on ascreen or a network), going through various muxers, demuxers, decoders and filters. Even the interfaces are plugins for LibVLC. It is up to the developer to choose which module will be loaded.

Modules are located in the modules/ subdirectory and are loaded at runtime. Every module may offer different features that will best suit a particular file or a particular environment. Besides, most portability works result in the writing of an audio_output/video_output/interface module to support a new platform (eg. BeOS or MacOS X).

Plugin modules are loaded and unloaded dynamically by functions in src/modules.c and include/vlc_modules*.h. The API for writing modules will be discussed in a following chapter. TODO

Modules can also be built directly into the application which uses LibVLC, for instance on an operating system that does not have support for dynamically loadable code. Modules statically built into the application are called builtins.