Netzflocken

First we had Mdm. Tussauds - and yes, despite Ryanair, we made it.

We landed 15:25 in Stansted, probably at the place with the furthest walking distance to the Stansted Express station, where we watched our train leaving at 15:45. The tickets for the house of wax have been valid for 17:00, with half an hour tolerance for entry, and they close a half past six. And the next train was scheduled for 17:03. So counting started again. Three quarters until Liverpool Station, finding a place for the luggage, getting a subway ticket and a tube to Baker Street - a tight schedule.

At Mdm. Tussauds we arrived 10 minutes after five, after I’ve spend £ 13,- at the left-luggage office. I forgot, no lockers anymore, the luggage was even x-rayed. :-/

But we had still plenty of time. Who is Humphrey Bogart or John Wayne? “Dad, lets go to Spiderman, and look, there is Captain Jack Sparrow.” As said before, different priorities. ;-)

After some fast-food in Liverpool Station and picking up our luggage again we arrived finally in our hostel, the Balham Lodge. A bit outside of the city, in the South West of London, but only a 15 minute ride and very reasonable priced. And wifi all over the building [Dad’s priorities 8)].

Next morning, after a plenteous mix of English and Continental breakfast, we headed for more adventures.

The London Eye! If you are into observation wheels it is a must! And even if you are not! And it pays of to buy the tickets in advance. So we even avoided the short queues at the tickets booths. We have been extremely lucky with our tickets at all. No queues, we just walked in at every place.

After the flight with on the Millennium Wheel we took a ride with the boat down the Thames to Tower Bridge and landed at the Tower embankment. There we appraised the Crown Jewels and examined of course every cannon in the armoury in the White Tower. Next we went to the Tower Bridge and the engine rooms there. That machinery making the bride move is still a great piece of engineering art.

Knackered as we were we could only manage a walk-by visit of St. Paul’s and headed back to the hostel and had a great dinner at an Indian restaurant nearby.

For Saturday I had arranged a sightseeing hop-on-hop-off bus tour that brought us around the city. This gave us enough time for Big Ben, Buckingham Palace, Picadilly Circus, Trafalgar Square, Whitehall, the Horseguards and Westminster Abbey. A police operation blocking a black mini-van the and barricading of the street by armed police men and the following personal search of the occupants and their luggage was the diversion during out our ice cream break at the upper end of St. James. Not that amusing for the people of the car who have been able to continue their journey after whatever that action was. Something similar on our way down Whitehall and the blocking of Bridge Street due to a bomb alarm had already some touch of normality.

Actually there haven’t been any five minutes in the city one hasn’t heard sirens or has seen police cars heading high-speed down the street. It’s thought-provoking.

We ended that day, after a detour at Covent Garden, with a traditional Fish and Chips take away at Fish Central.

In his last year he took a supplementary English class and he learnt a lot about London and the sightseeings there. I thought giving him the chance to see these in real and visit them is a nice reward.

And so we are now today on our trip to London. But unexpectedly stopped at the airport in Frankfurt/Hahn due to delayed Ryanair flight FR755. Instead of leaving at 11:40 new departure is expected to be around 15:00.

Ryanair is btw not providing any water or food to ease the delay a bit. :-(

Anyway, I hope that we depart really at 15:00 as I have prebooked tickets for Mdm. Toussauds in the late afternoon. We could still manage that if we rush from the airport directly to the wax-museum, leaving our luggage at Liverpool station.

Great start for a leisure trip. ;-)

I think it is the last one that needs the beta label. The core is faily stable now, don’t think that there are too many quirks lurking there.

New in this release are:

• integration of a new logging module

  logging can now be configured via the config file or through an environment variable COHERENCE_DEBUG, which overrides the config values. Usage is like:

  COHERENCE_DEBUG=*:3
  - emit INFO level messages from all modules

  COHERENCE_DEBUG=*:2,ssdp:4
  - WARNING level messages from all modules, plus debug level for the ssdp module

• removed the dependency for SOAPpy, now using own methods and ElementTree only

• start reworking the client API, to make things there easier too, see as an example the new Coherence MediaRenderer

• serving cover art now to DLNA MediaRenderers

• refinements on the object creation and the import into the MediaServers

• an installable package for the Nokia Maemo platform on the N800, complete with all dependencies, thanks to Rob Taylor of CodeThink

• and a lot more of the usual bugfixes and enhancements

For version 0.5.0 I have in mind

• some first form of D-Bus integration to simplify the integration of with non-Python applications

• rework of the client API

• UPnP tests - and tests for Coherence itself - with the toolset micxer is working on

The intention of the talk was to give a quick overview about DLNA/UPnP and to spread the word to the Gnome developers that there is something that allows an easy connection of their own software.

You can get the slides from the Coherence site.

The talk itself went reasonable well - mostly due to the fact that Jono, keeper of the chicken watch, was very, very generous with the assigned time for it.

So if you have missed it there or just want to know a bit more about DLNA and UPnP, and why I think it is important to use these stacks within Linux multimedia applications, grab it while the electronic ink is still stabilizing.

PS: I was asked if I could to a more detailed talk, so maybe there will be one next year at the Fosdem in Brussels.

I did it!

Today I tagged the 0.1.0 release of Coherence and made it public with an entry in the Python Cheeseshop, and it got downloaded already several dozen times.

During the next days the new Elisa release will get announced too, using now, aside from the UPnP MediaServer, Coherence for the UPnP client too.

Somehow I’m now waiting in suspense for new bug reports – not too many I hope , feature requests and new ideas on what to change, to improve or to enhance.

Things that are on the list for the next releases:

• improve the web UI so we get closer to a web-based UPnP ControlPoint
  
  For now we just show all found devices, but thanks to Athena at least in real time when they announce or log off themself.
• testing of other devices, a first step into the Intel UPnP Device Spy direction
• “port” Coherence to the Maemo platform, so we’ll can use the UPnP MediaServer and the UPnP MediaRenderer on the Nokia N800
• switching to Flickrpc - Ross Burtons Twisted based Flickr library
• start with a DAAP->UPnP bridge and export in a first step DAAP provided content via UPnP

Thanks to Nokias generosity I now have the possibility to test Coherence with and against the UPnP stack shipped with the N800 and used e.g. by Media Streamer or Canola and the UPnP plugin for the gnome-vfs layer.

So far I used the file manger application and Media Streamer, and there have been pleasant and promising results.

The Coherence powered devices are spotted by the N800 and the content retrieval from the MediaServers - even the Flickr one - works fine.

Albeit from the file manger application which seems to circle sometimes.

The GStreamer MediaRenderer backend is recognized too and can be controlled, with the restriction that the Media Streamer UI does not follow the state changes. I’m still unsure whether this is on behalf of Coherence or on the Media Streamer side, but whatever it is, it can’t be anything more than a mere nothing.

Meaning we are probably only one little bug apart from being able to control Elisa with the N800.

Regarding Media Streamer acting itself as a controllable MediaRenderer, there it is fallen a bit short of my expectations, as it doesn’t provide anything at all – neither controlling nor eventing.

That’s definitily another good reason to get Coherence up and running on the Maemo platform.

PS: If your are like me looking for something to take a screenshot on the N800, I have been lucky with load-applet-run, and I was told @ irc://freenode.net/#maemo that the Maemo screen grabber together with the osso-screenshot-tool should work too.

The XBox 360 UPnP client is a little bit peculiar and finicky regarding its dealings – well, actually it only wants to talk to its really close friends, the Windows Media Player 11 and the Windows Media Connect server.

With a lot of patient care from Tristan Seligmann and a yet unknown contributor we managed to win its confidence and now that poor little thing has started to talk via UPnP to Coherence – and requests so far audio and image files from the MediaServer, even from the Flickr backend.

To be honest, it was more the devotedness of Coherence than the willingness of the XBox that made this happen, especially when it came to the UPnP idiom spoken in the suburbs of Seattle, but anyway it is a nice thing to see this cagey behaviour come to an end.

And what’s even greater to see is Coherence being of real use for somebody outside and furthermore getting something back!

As a follow-up to my last post about the GStreamer backend for Coherence I’m happy to announce now the Coherence Flickr UPnP A/V MediaServer backend.

What does it do:

1. it connects to Flickr via the Flickr API and enquires a list of interesting photos for the most recent day
2. it provides that list via the ContentDirectory service to other UPnP A/V enabled devices

So if you have such a multi-functional home-automation touch-panel like mine or one of these tvs with a build-in UPnP A/V client you can now enjoy an ever changing stream of photos coming to your living room.

Of course there will be Flickr enabled picture frames popping up from every manufacturer climbing on the bandwagon - which will definitly have their right to exist, especially if they are used in a isolated environment - but if you are in a connected home it sounds unreasonable to supply configuration to every device all over the place.

Hence the charm of these few lines of Python code lies in its possibility to make Coherence the one-stop-shopping media gateway.

I’ll add a few more features over the next days:

• enquire user, group or tag based photo lists
• optionally only show photos in landscape format
• define picture quality to download
• make the number of photos returned configurable, currently it is limited to 100
• recheck with the Flickr service every e.g. 180 minutes and fetch new photo urls
• maybe act as a proxy to Flickr for devices which are not able to connect to something outside the home lan

And something I would like to add too, but this will take some more time, is a mapping between the UPnP ContentDirectory ImportResource() and CreateObject()/MoveObject()/… actions to the Flickr upload API.

In an attempt to work on the documentation and as a practice finding the words to explain how Coherence ticks I’ll try to throw some light on how the GStreamer playbin backend and Coherence are glued together to form an UPnP A/V MediaRenderer device.

A device in UPnP speak is a logical something - a grouping of services. A MediaRenderer as an example needs to support

• a RenderingControl service, which is responsible for adjustment of volume, loudness, brightness,…
• a ConnectionManager service, used to enumerate and select the transfer protocol (http, rtsp/rtp,…) and
  data format (mp3, ogg,…) to be used for transferring the content
• an AVTransport service, optional - depending on the transfer protocols the ConnectionManager supports. But if available used to specify the content to be played, start/stop/pause a playback, seek in the content stream,…

These services can be controlled and queried with so called Actions, e.g. SetVolume() and GetVolume(), and hold their current state in so called StateVariables, e.g. Volume. A call to SetVolume() sets the volume value on the actual rendering engine and reflects that change in the variable Volume. And a call to GetVolume() retrieves the value from that variable. Furthermore a service is supposed to propagate the values of these variables on change to interested parties, e.g. to an UPnP ControlPoint.

Now one of the basic principles of Coherence is to seal off the backend – the actual rendering engine, in this case the GStreamer playbin – from the UPnP related tasks (and later from the D*AP ones) as much as possible.

This means that a backend should only need to

1. tell Coherence what kind of device(s) it wants to resemble, e.g. a MediaRenderer
2. define specific conditions, e.g. that is supports only decoding of mp3 content
3. provide methods Coherence can access when an action is called that has effects on the backend engine, e.g. a volume change
4. inform Coherence about state changes, e.g. the end of the media content is reached and playback has stopped

Everything else is the job of Coherence:

• propagate the device on the network (SSDP/MSEARCH)
• generate the necessary device and service descriptions with reasonable defaults, corresponding to the backends capabilities
• provide the control interfaces to the actions the services have
• handle all event subscription and propagation tasks (GENA)

This means also, that all actions with no effects on the backend engine are handled completely within Coherence, like an action that retrieves only a variable value. Of course a backend can override this if it wants to, but basically there is no need to do it.

In our GStreamer playbin case this (simplified) looks like this:

class Player:

    """ see item 1. above """
    implements = ['MediaRenderer']

    """ see item 2. above """
    vendor_value_defaults = {'RenderingControl': {'A_ARG_TYPE_Channel':'Master'},
                             'ConnectionManager': {'SinkProtocolInfo', 'http-get:*:audio/mpeg:*'}}
    vendor_range_defaults = {'RenderingControl': {'Volume': {'maximum':100}}}

    def __init__(self, device):
        self.player = gst.element_factory_make("playbin", "myplayer")
        self.device= device

    def set_volume(self, volume):
        """ here the actual volume change takes place """
        """ gstreamer playbin has a volume range from 0.0-10.0 """
        self.player.set_property('volume', float(volume)/10)

         """ feed back the new state - our item 4. """
        rcs_id = self.device.connection_manager_server.lookup_rcs_id(self.current_connection_id)
        self.device.rendering_control_server.set_variable(rcs_id, 'Volume', volume)

    def upnp_SetVolume(self, *args, **kwargs):
    """ that's a method referred in item 3. """
        InstanceID = int(kwargs['InstanceID'])
        Channel = kwargs['Channel']
        DesiredVolume = int(kwargs['DesiredVolume'])
        self.set_volume(DesiredVolume)
        return {}

This is not perfect and not final yet and there will be some changes especially in the way how item 4. is handled. But the purpose of that backend is among other things to straighten out the bumpiness of these glue points.

And btw., in this backend the engine is embedded, but as stated in an earlier post, there is absolutly no reason why instead of calling self.player.set_property to set the volume this couldn’t be some ipc call (xml-rpc, dbus, Twisted PB,…) or an IR/ZigBee/ZWave signal emitted.