Difference between revisions of "Old Python bindings"

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m (moved Python bindings to Old Python bindings: There are new python bindings (ctypes-based). Preserve this information for the moment, as the old bindings are still used.)

Revision as of 13:57, 4 September 2009

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 developed, based on the MediaControlAPI. It can be found in bindings/python.

Sources are browsable from python binding and a code sample can be found in the sources (file vlcwidget.py).

It has been compiled, and is being used, on Linux, Windows and Mac OS X.

Compile HOWTO

Only for < 0.9.0 versions: If you want to include the python bindings in your build, you must pass --enable-python-bindings (svn version) or --enable-mediacontrol-python-bindings (0.8.6* versions) to ./configure as it is disabled by default.

For >= 0.9.0 versions, python bindings cannot be compiled at the same time as the main VLC tree. They can (and event must) be compiled from a compiled VLC, provided that appropriate headers and libraries (libvlc.so/.dll) are available.

Linux/Debian

On Debian:

  • install the libvlc2-dev package
  • Get the python bindings sources from the Git repository :
  • in the python directory, launch
 python setup.py build

The module will be built in build/lib.linux-i686-2.5

  • install the module through (as root)
 python setup.py install

or simply copy the vlc.so file to some appropriate directory.

Windows

 python setup.py build --compiler=mingw32

You should get a vlc.pyd (or vlc.dll) file in the build/ subdirectory.

Basics

The vlc python module provides 4 main classes : MediaControl, Instance, MediaPlayer and Media.

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.

vlc.Instance, vlc.MediaPlayer and vlc.Media match the new LibVLC API. Refer (for now) to the docstrings provided by the python objects to get their usage.

Tips and tricks

Building notes

  • on 0.8.6(a), the --enable-mediacontrol-python-bindings option is not compatible with --enable-libtool. If you need libtool support, please use the svn version.

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 --clone-vout-list default,snapshot --snapshot-width 320 --snapshot-height 200".split())

Advantages of the old (filter-based) approach:

  • 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.

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, since VLC will look for its plugins in the current directory. Another way is to pass the correct --plugin-path option.

   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()

Source code