This page provides a quick VLC architecture overview. Follow the links for a deeper exploration.

VLC Application, Core Library, Modules

The VLC Media player is made of:

• the VLC application (there are several versions) : it is built on top of libVLC.
• the VLC Library (libVLC) : It exposes a public API to build applications on top of VLC Core.
• the VLC Core Library (libVLCcore) : It manages the threads, the modules (codecs, demuxers, etc...), the modules' layers, the clocks, the playlist and all low-level control in VLC.
• the VLC Modules : VLC uses modules to do most of the work at every stage (various muxers, demuxers, decoders, filters and outputs). Modules are built against libvlccore.

More information can be found on the VLC developer site.

User interfaces

Several VLC user interfaces are available, implemented by dedicated modules.

• qt, libqt_plugin.la : the default user interface for windows and linux. It uses the Qt Library.
• macosx,libmacosx_plugin.la : the native interface for MacOS.
• skins2, libskins2_plugin.la : the skinnable interface for Linux/MacOS/Windows.
• ncurses, libncurses_plugin.la : the text / command line interface. It uses the ncurse library.
• lua, liblua_plugin.la which exposes HTTP and TELNET interfaces. see also the web interface content.
• rc, liboldrc_plugin.la : remote control, this seems deprecated.

libVLCcore creates the interface: see intf_Create in interface.c.

• On Windows, the qt module is declared with set_capability( "interface", 151 ): See qt.cpp.
• As 151 is the highest score compared to other interface modules, qt is the default interface.

Modules (Plugins)

Each module belongs to a category (main and sub): these categories are defined in vlc_plugin.h: Interface, Audio, Video, Input, Output, Advanced, Playlist.

More importantly, a module exposes capabilities (described by a string) associated to a score (module priority), like 'interface', 'decoder', 'audio output'. See Videolan wiki for details.

Starting VLC and playing a media file

The following sequence is indicative.

• The program starts: bin/vlc.c, main function is executed. It creates a new libvlc instance ( libvlc_new, function implemented by libvlc )
• src/libvlc.c, libvlc_new calls libvlc_InternalInit, which initializes VLC. This creates a user interface (libvlc_InternalAddIntf). This function starts the playlist with its control thread (intf_GetPlaylist) and creates the user interface (intf_Create). If there is a command line argument to open a file, libvlc_InternalInit inserts the item in the playlist (intf_InsertItem)
• In the QT user interface (running with its own Interface thread), the Open dialog is used to select the file. See modules/gui/qt/dialogs/open.cpp. The file is put into the queue, see play and enqueue
• the media resource is added to the playlist, see src/playlist/input.c, playlist_AddExt function
• the playlist runs with its own control thread. See src/playlist/thread.c. playlist_Activate starts the thread; Thread is the main function with the playlist high level tasks.
• the playlist control thread plays the items. The PlayItem function creates an Input and starts it.
• the input starts in its own input thread, either to preparse or play/run the media. See input_Start in src/input/input.c
• the input MainLoop runs. This calls InputSourceNew, then InputDemuxNew to initialize an access-demux module (2 in 1), otherwise an access and demux modules are created.
• src/input/demux.c: the demux_NewAdvanced function gets a demux module to seperate the streams (in container files like AVI or MKV): module_need( p_demux, "access_demux", ...
• if no access-demux module: src/input/access.c. The access_New function gets an access module to read the input stream (from a file, http, ...): module_need(access, "access", ...
• the demuxer module adds the tracks (this creates the decoders). For example, see modules/demux/avi/avi.c: static int Open( vlc_object_t * p_this ) function.
• src/input/decoder.c, decoder_New creates a decoder and spawns a decoder thread . LoadDecoder function, gets a decoder module (audio, video or spu): module_need(decoder, caps[decoder->fmt_in.i_cat], ...) /* "video decoder" or "audio decoder" or "spu" */
• the video decoder requests a video output ( input_resource_RequestVout )
• src/video_output/video_output.c, VoutCreate function, spawns the Video output Thread, this will lead to the video output creation.
• src/video_output/display.c, vout_display_New function, gets a "vout display" module: module_need(vd, "vout display",...
• the audio decoder requests an audio output ( input_resource_GetAout )
• src/audio_output/output.c, aout_New function, gets a "audio output" module: module_need (aout, "audio output",...