MediaControlAPI

Description

The MediaControl API is the extended API to control VLC from external applications (extension of LibVLC). Its core part (playback control) has been taken from the OMG Audio/Video Stream specification, and extended with additional functionalities. An IDL specification MediaControl.idl has been the base of this work.

The idea is to define a generic video-player API, that could be reused with other players.

The API is defined in "include/vlc/control.h" and implemented in "src/control".

The Doxygen documentation can be found at [1].

Current status

The API currently includes functions for the following things:

• Playback
  • Basic features (play/pause/stop)
  • Seeking
  • Basic playlist interaction
  • Stream information
• Audio/Video
  • Snapshot control (requires the use of the snapshot vout module via the clone video filter; invoke with: vlc --video-filter clone --clone-vout-list default,snapshot )
  • OSD display (of text and SVG graphics through the svg rendering module)
  • Volume setting
  • Setting the visual ID of an embedding window

Current uses

The MediaControl API is used by the following modules :

• the PythonBinding
• the CORBA interface module
• the JavaBinding

Foreseen evolutions

The following evolutions should be integrated in the API, but discussion is necessary to ensure that they are sufficiently flexible to match various needs :

• sound_[sg]et_volume: normalize volume in [0..100]
• implement get_aspect_ratio (or get_dimensions ?)
• implement get_api_version() or get_capabilities() (which would return the list of capabilities supported by the player: ("core", "svg", "snapshot", etc)
• implement get/set_rate()
• Complete the implementation. For instance, the frame-by-frame unit (mediacontrol_SampleCount) is not implemented, and the stop/pause do not take the Position parameter into account (they are applied immediately).
• Fix VLC initialization on Win32 so that it uses the registry key to find the default plugins directory by default. Currently, it uses the vlc.exe path, which it cannot find when using VLC embedded. A workaround is to chdir to the vlc.exe directory before instanciating the MediaControl() object.

Todo

• Add missing features (see next section)
• Bind the new API to .NET

Full API

Initialization

• mediacontrol_new Create a new instance of a MediaControl object
• mediacontrol_get_version Return the version of the API
• mediacontrol_new_from_object(object_id) Use an existing VLC object id to initialize the MediaControl object
• mediacontrol_exit Stop VLC

Playback control

• mediacontrol_start( position )
• mediacontrol_pause( position )
• mediacontrol_resume( position )
• mediacontrol_stop( position )
• mediacontrol_get_media_position
• mediacontrol_set_media_position
• mediacontrol_set_rate

Media info

• mediacontrol_get_stream_information Return synthetized information (position, url, status), so that applications can quickly get it (Advene for instance calls this method every 100ms)
• mediacontrol_get_video_information Return misc. information about the video (aspect ratio, dimensions, bitrate, codec, author, etc). The output could be transmitted in some generic format (XML?)

Playlist

• mediacontrol_playlist_add_item ( MRL ) should return item id
• mediacontrol_playlist_clear()
• mediacontrol_playlist_get_list
• mediacontrol_playlist_next
• mediacontrol_playlist_prev
• mediacontrol_playlist_play( id )
• mediacontrol_playlist_remove( id )
• mediacontrol_playlist_sort( int ) <- int is a const, the rule to sort with

Could be transformed into a Playlist object (returned by MediaControl.playlist), that would feature the corresponding methods: add, clear, next, prev, play, sort... -- OlivierAubert

Video

• mediacontrol_snapshot(position) <-- returns an RGB picture should probably use vout_Snapshot instead of the snapshot module (but cf discussion in [VoutReworkUserRequirements] and [PythonBinding])
• mediacontrol_all_snapshots()
• mediacontrol_display_text( text, start_time, stop_time )
• mediacontrol_set_visual(visual_id)
• mediacontrol_toggle_fullscreen
• mediacontrol_apply_filter ( filter, position ) <-- is there a filter structure in VLC? And isn't that too VLC-specific ? The rest of the API (minus suggested VLM, which is clearly identified) is fairly generic. We could move vlc specific features in an 'extra' module.

Audio

• mediacontrol_sound_get_volume
• mediacontrol_sound_set_volume
• mediacontrol_sound_mute

VLM

• mediacontrol_vlm_add_broadcast( name, input, output, options)
• mediacontrol_vlm_add_vod
• mediacontrol_vlm_get_broadcasts
• mediacontrol_vlm_get_vods
• mediacontrol_vlm_delete_broadcast( name )
• mediacontrol_vlm_delete_vod( name )
• mediacontrol_vlm_load( file )
• mediacontrol_vlm_save( file )