[vlc-devel] Re: [Banshee-List] [bmpx] Re: Proposal for a common D-Bus interface for media players

Brian Nickel brian.nickel at gmail.com
Wed Dec 6 19:20:03 CET 2006

For running multiple media players, wouldn't it be easiest to have each
player have its own DBus object that implements the common library (with
their own player specific features on top) and in addition have a second
common DBus object "org.freedesktop.MediaPlayer" which points to the
object or contains the object (I have little knowledge of how DBus
works), so that when a player starts up it can launch its own DBus
object and then attempt to take control of the universal name. If it
fails to get the universal name, it will still work, but no calls to the
universal name will get to it, just direct calls to its own object.

I hope that made sense.

- Brian

On Wed, 2006-12-06 at 06:04 +0100, Milosz Derezynski wrote:

> Allright as i've read on the transcript, you're going to implement the
> DBus interace as a "client" anyway.
> So for one: nevermind the part about "DBus or nothing", but then again
> what is your concern with running one player, and debugging XMMS2 the
> same time? 
> Milosz
> On 12/6/06, Milosz Derezynski <internalerror at gmail.com> wrote:
>         Sham:
>         Yeah it would basically mean that one player can run at a
>         time, but going with what Diego said earlier, i'd concur that
>         it could be very well something that is not directly at the
>         core of the application, and it can be started without
>         exposing itself through DBus. BMPx can do this in fact if you
>         start it with the -bin binary and pass --no-remote to it. 
>         (For those unfamiliar with what i mean with -bin binary: BMPx
>         implements a
>         single-application-instance/application-as-service [1]
>         mechanism using DBus activation. There is a 'remote' binary
>         which is for all intents and purposes for the user just like
>         the main application binary, and a "-bin" binary (similar to
>         firefox-bin for firefox/comparable) in libexec) 
>         Furthermore, and i'm aware i might be digging up probably
>         unpleasant stuff i see the problem with XMMS2+DBus the one
>         that there is no "real" reason for XMMS2 to not switch to DBus
>         (yeah i know about tru's technical explanations and the
>         don't-broadcast and no TCP/IP transport stuff but that will
>         appear, well anyway back to the main sentence), so, basically,
>         once XMMS2 implements a DBus interface using this common spec,
>         there would be no _real_ reason to not to switch to DBus
>         entirely for server<->client messaging (XMMS2 to clients for
>         those not in the know). 
>         So either this will happen (you switch entirely), or you guys
>         will just not switch to DBus at all; everything else is just
>         unfeasible if not at the very least from a maintenance point
>         of view, and it would be obviously also hilarious because of
>         other reasons to implement 2 very similar systems of which
>         either could replace the other (except that without DBus,
>         there will be hardly a common interface implemented.) 
>         I just want to point this out right now and bring it to the
>         surface, before we all start a chanty dance around an empty
>         pot.
>         Everyone:
>         As for the table, it's something Sham has done some good while
>         ago and it's a good starting point to see how common the
>         current interfaces are. 
>         Sham (again):
>         Can you wiki-fy the table and make it editable (perhaps only
>         on request and only for people you approve for, well, namely
>         the media player developers or the players listed there at the
>         least, so we can quickly amend it, etc.. ? 
>         Regards,
>         Milosz
>         [1] http://live.gnome.org/DesktopAppsAsDBusServices (NOTE: We
>         actually deployed this mechanism 1 year before Alex proposed
>         it in his form, so our implementation differs in details, but
>         is essentially the same; it doesn't go -as- far as putting
>         stuff into .desktop files that could be regarded as bogus
>         until really accepted as a spec/way to do things) 
>         On 12/6/06, Sham Chukoury <eleusis at xmms.org> wrote:
>                 Hello world.
>                 Seb Ruiz wrote:
>                 > Actually, whilst I was in san francisco, I spoke
>                 with the xmms2 folks
>                 > about the same thing. we totally agreed on the
>                 necessity for it.
>                 Indeed, this was discussed a bit during a meeting:
>                 [1] 
>                 (full transcript at [2])
>                 >> I've been working recently of a D-Bus [2] control
>                 interface for VLC,
>                 >> to permit other applications to interact with VLC.
>                 >> This implements basic functions such as: 
>                 >>         - playback control (Play/Pause/Next..)
>                 >>         - information on medias (Meta-data/Length)
>                 >>         - playlist editing (Add new elements to
>                 play)
>                 >>
>                 >> I've been looking at how other media players
>                 already implemented that, 
>                 >> and I thought all their interfaces were highly
>                 redundant, and could
>                 >> benefit of implementing a single, common, shared
>                 interface.
>                 >>
>                 >> That would let developers use this interface in
>                 their programs, and 
>                 >> let their users decide of which media player they
>                 wanna use. All about
>                 >> FREEDOM.
>                 I've done a bit of work on this, though in the form of
>                 a Python library (Chalyx
>                 - for XMMS2 [3] and MPD [4] clients), not an open spec
>                 or interface of any kind. 
>                 You can see the class defining the methods to be used
>                 at [5]
>                 It's a bit of a compromise between the interfaces
>                 provided by XMMS2 [6] and MPD
>                 [7] (though biased a bit towards XMMS2). You can see a
>                 table comparing the 
>                 interfaces at [8] (Some MPRIS/BMP/BMPx calls are
>                 included, but they've never
>                 been implemented in Chalyx)
>                 >> I've copied this specification on the videolan wiki
>                 [6], and modified
>                 >> it to my needs. I tried to keep it as general as
>                 possible. However 
>                 >> this still needs more work, and comments.
>                 >>
>                 >> This is why i'm reaching you, developers of some
>                 media players, to
>                 >> comment what i've done or work with me, until that
>                 specification 
>                 >> fulfills your needs, and can be used in a real
>                 world.
>                 >>
>                 >> This specification should stay as generic as
>                 possible, because media
>                 >> players that want to make specific methods
>                 available with D-Bus can do 
>                 >> it through their specific interface.
>                 >>
>                 >> For example, basic methods would be available on
>                 the service
>                 >> org.freedesktop.MediaPlayer and VLC would make
>                 streaming methods
>                 >> available on the service org.videolan.vlc. So, a
>                 basic control applet
>                 >> for the KDE panel originally written for amarok
>                 would be able to
>                 >> control VLC, and a complex pygtk script would
>                 control streaming
>                 >> features of VLC. 
>                 Re: 'The Service' on the DBus-spec page, am I to
>                 understand that only one player
>                 supporting the spec may be running at any one time?
>                 That makes sense from the
>                 point of view that the user might want a single
>                 'default' player to control, but 
>                 what if the user wants 2 such players running at a
>                 time? For example, listening
>                 to music using VLC while debugging XMMS2? ;)
>                 Re: generic interface, does that mean there could be
>                 standard interface
>                 extensions? For example, players with access to a
>                 media library could have an 
>                 extended interface
>                 'org.freedesktop.MediaPlayer.Library'.
>                 Cheers.
>                 -S
>                 [1]
>                 http://wiki.xmms2.xmms.se/index.php/IRC_Meeting/2006-11-27/Minutes#Amarok_and_XMMS2_Collaboration
>                 [2]
>                 http://dan.chokola.com/files/xmms2-meeting/2006-11-27/transcript.txt
>                 [3]
>                 http://xmms2.xmms.se/epydoc/public/xmmsclient.XMMS-class.html
>                 [4]
>                 http://mpd.wikia.com/wiki/MusicPlayerDaemonCommands
>                 [5]
>                 http://git.xmms.se/?p=chalyx-eleusis.git;a=blob;f=src/Chalyx/services/service.py
>                 [6]
>                 http://git.xmms.se/?p=chalyx-eleusis.git;a=blob;f=src/Chalyx/services/xmms2.py
>                 [7]
>                 http://git.xmms.se/?p=chalyx-eleusis.git;a=blob;f=src/Chalyx/services/mpd.py
>                 [8]
>                 http://xmms2.xmms.se/~eleusis/misc/client-api-table.html
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