Old Python bindings

Python binding documentation

For a while, there has been a basic python binding for libvlc (located in vlc/pyvlc), that was used for streaming. A more complete (with a hopefully generic API that can be reused by other players) has been developped, based on the MediaControlAPI. It can be found in vlc/bindings/mediacontrol-python.

Sources are browsable from python binding and a code sample can be found in [1].

It has been compiled, and is being used, on Linux and Windows. It compiles and run on Mac OS X, but embedded vout support is under development in VLC.

Basics

The vlc python module provides 2 main classes : MediaControl and Object.

vlc.Object provides a binding to the vlc object architecture. It allows to manipulate variables and configuration options, and explore the object hierrarchy. The vlcdebug.py script, located in the python bindings directory, wraps around the vlc.Object to provide an easier access to variables and objects (as illustrated in the code sample in [2]).

vlc.MediaControl implements the MediaControlAPI.

Methods taking positions as parameters expect a vlc.Position object, that provides a very flexible way to address absolute or relative positions, in a number of units (milliseconds, frames or bytes). For convenience, the python binding automatically converts integer positions into milliseconds vlc.Position objects.

Tips and tricks

Python specificities

The python bindings provide a binding for the [MediaControlAPI], with some variations :

• the methods taking a vlc.Position parameter also accept an integer, which will then be converted to a relative position in milliseconds (vlc.MediaTime)
• the start, stop, pause and resume method position parameter is optional. If omitted, it will default to a 0-relative position.
• RGBPicture (returned by snapshot) and StreamInformation (returned by get_stream_information) are not objects with attributes, but instead dictionaries.

Snapshot support

In the current svn revision, we use the core snapshot functionality of vlc, which is simpler to setup (no additional module, see below) and directly returns PNG, but less precise.

Prior to revision 13881, in order to get snapshot support, you had to activate the snapshot vout module through a clone video filter. The following code gives a way to achieve this :

 mc=vlc.MediaControl([ "--vout-filter", "clone" ])
 o=VLC.Object(0)
 o.config_set("clone-vout-list", "default,snapshot")
 o.config_set("snapshot-width", 320)
 o.config_set("snapshot-height", 200)

Note that all config options could have been given on the command line, but this illustrates the use of the vlc.Object API.

There is a snapshot functionality built in the vlc core, associated to a hotkey. The MediaControlAPI could (should ?) use it, but

• it did not exist at the time the extension was developped
• the snapshot vout module holds a cache of reduced-size snapshots, that allow to take into account the reaction time of the user (around 200ms) and also to precisely select the more appropriate snapshot from the cache.
• the builtin snapshot functionality is oriented towards interactive use (hotkey activation, saving into a file) and should be revamped to take into accound a more programmatic use [Note: this is now implemented, cf src/video_output/vout_intf.c, and look for "object-id"]

Win32 initialization

If the vlc module was not compiled with the exact same prefix as the VLC installation (e.g. c:\\Program Files\\Videolan), then it cannot find itself the installation directory (stored in the registry Software\VideoLAN\VLC\InstallDir), and the MediaControl instanciation will fail with a message like "Cannot find interface plugins".

The workaround consists in changing directory to the VLC installation directory before instanciating the MediaControl object.

   def get_registry_value (self, subkey, name):
       import _winreg
       value = None
       for hkey in _winreg.HKEY_LOCAL_MACHINE, _winreg.HKEY_CURRENT_USER:
           try:
               reg = _winreg.OpenKey(hkey, subkey)
               value, type_id = _winreg.QueryValueEx(reg, name)
               _winreg.CloseKey(reg)
           except _winreg.error:
               pass
       return value
   
   vlcpath=get_registry_value('Software\\VideoLAN\\VLC','InstallDir')
   if vlcpath is None:
       print "Cannot locate VLC installation directory"
   else:
       os.chdir(vlcpath)
       mc=vlc.MediaControl()