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During the past few months I’ve been occasionally working on integrating GStreamer better with wayland. GStreamer already has a ‘waylandsink’ element in gst-plugins-bad, but the implementation is very limited. One of the things I’ve been working on was to add GstVideoOverlay support in it, and recently, I managed to make this work nicely embedded in a GTK+ window.

GStreamer Wayland GTK Demo

gtk+ video player demo running on weston

I’m happy to say that it works pretty well, even though GTK does not support wayland sub-surfaces, which was being thought of as a problem initially. It turns out there is no problem with that, and both the GTK and GstVideoOverlay APIs are sufficient to make this work. However, there needs to be a small addition in GstVideoOverlay to allow smooth resizing. Currently, I have a GstWaylandVideo API that includes those additions.

This essentially means that as soon as this work is merged (hopefully soon), there is nothing stopping applications like totem from being ported to waylandūüėÄ

I believe embedding waylandsink in Qt should also work without any problems, I just haven’t tested it.

If you are interested, check the code. The code of the above running demo can also be found here, and the ticket for merging this branch is being tracked here.

I should say many thanks here to my employer, Collabora, for sponsoring this work.


Hello all! Long time no blog. The reason I decided to blog this time is that I want to spread the word about CommonsFest, a different festival that will take place in less than two weeks (9-11 May) in my home city, Heraklion, in Crete.

What is it?

CommonsFest-Logo-BlueCommonsFest is a festival that aims to promote freedom of knowledge (or free knowledge) and peer-to-peer collaboration for the creation and management of the Commons. A philosophy that has spread through free software communities and extends to many aspects of our daily lives, such as the arts, governance, construction of machinery, tools and other goods. In other words, it aims to raise the awareness of people about the philosophy of open source in its generalisation, involving open source code, open hardware, creative commons and similar initiatives like open source ecology, open governance, etc.


This festival was conceived and organized for the first time in Heraklion last year by a group of volunteers, myself being one of them, who felt that it is worth promoting this philosophy to people that are unaware of its existence, especially in this time of economic crisis where it is clear that people need to cooperate more and share in order to go forward. This year we are repeating it, aiming to be better and achieve even more. Our long term vision is to spread this philosophy to as many people as possible around the world and eventually improve our lives by changing the way people think. We believe in this idea that the world would be a better place if we all shared our knowledge and worked together, equally, for the well-being of all of us.

I love the idea, how can I be part of it?

There are many ways you can help. First of all, this year, the festival is crowd-funded to cover our expenses (mainly printing and transportation for the speakers). If you like the idea and would like to support us directly, you could give a small donation. Another way you can help is to just share this with other people that may (or may not) be interested – even if it’s just to raise their awareness about the subjectūüėČ. Finally, you could help to achieve our goals by organizing something similar in your area. All our material (logos, texts, slideshows, etc) is freely licensed under creative commons licences, so you can also use them if you want.

Where can I learn more?

Have a look at our website, our fund-raising campaign, our facebook, google+ and twitter pages. You can also contact the organizing team by email.


Video calls in KDE-Telepathy

Well, I think I owed you this oneūüėČ Remember back in 2009 when I was working on KCall¬†as part of the GSoC program? Well, it may have taken 2.5 years more, but I’m now pleased to announce that it’s finally in a ready-to-use state \o/ Don’t expect it to be perfect, of course. It still has a long way to go.

Here is the obligatory screenshot. Me on my desktop, calling myself on my laptop:)

Screenshot of ktp-call-ui

The KDE-Telepathy call-ui in action

A little bit of history

When my GSoC finished in 2009, there were 2 main problems with KCall. The first one was that the bits of the telepathy specification for doing calls (i.e. the “StreamedMedia” channel type) were problematic, not to mention that the API of the telepathy-farsight library, which was the only way to use StreamedMedia, was also weird and it took me too many tries to finally understand it (in late 2010…), which in simple words means that KCall was very unstable beacause it used the API in the wrong way (if there really was a right way to use it…). The second problem was that there was no telepathy integration in the KDE desktop, so KCall would need to have a proper contact list, account manager and other stuff that it shouldn’t have to implement.

In late 2010, the KDE-Telepathy project started evolving and we finally managed to make a first release last summer with the necessary components to use telepathy on the KDE desktop. At about the same time, work began on a new API for doing calls in telepathy, the so-called “Call” channel type, plus telepathy-farstream, the new and enhanced version of telepathy-farsight. It took a little longer than expected, but finally a few weeks ago, thanks to the awesome work of my colleagues at Collabora¬†who engineered the whole thing, the “Call” API and telepathy-farstream were finished and released.¬†Fortunately, last year I had already worked on porting the call-ui to the draft Call API, using the draft telepathy-qt Call bindings that used to be in the telepathy-qt4-yell module. So, now I only had to first update the telepathy-qt bindings to the latest and greatest API specification and then do the same with the call-ui, plus fix a bit the UI, which was way too ugly. And so I did.

The present and the future

The UI is far from perfect at the moment, but the engine seems to work reliably. I have many additions and improvements in mind. However, since I suck at UI design, I’d love having mockups of ideas from people that can actually design UIs. And I’d also love having other people to implement those ideas, since I’m a lazy man…ūüėõ (ok, I don’t really mean that). So, if you feel like helping (either way), this is your chance to get involvedūüėČ

The current UI will be included in the next KDE-Telepathy release, 0.4, which is scheduled for next month. Be prepared.

Try it

So, if you can’t wait for the next KDE-Telepathy release and want to try this now, what you need is the latest ktp-call-ui from git master with all of its dependencies. To make a call, simply right click one of your contacts in the contact list and click “audio call” or “video call”. Alternatively, you can do this directly from the text-ui or the contact plasmoid. Note that older versions of those components also have audio/video call buttons, but they will try to start StreamedMedia calls instead, which will fail. Also note that calls require XMPP (jabber, google talk) at the moment, but SIP support is also on its way upstream.

During the past month I’ve been working on a new GStreamer element called qtvideosink. ¬†The purpose of this element is to allow painting video frames from GStreamer on any kind of Qt surface and on any platform supported by Qt. A “Qt surface” can be a QWidget, a QGraphicsItem in a QGraphicsView, a QDeclarativeItem in a QDeclarativeView, and even off-screen surfaces like QImage, QPixmap, QGLPixelBuffer, etc…¬†The initial reason for working on this new element was to support GStreamer video in QML, which is something that many people have asked me about in the past. Until now there was only QtMultimedia supporting this, with some code in phonon being in progress as well. But of course, the main disadvantage with both QtMultimedia and phonon is that although they support this feature with GStreamer as the backend, they don’t allow you to mix pure GStreamer code with their QML video item, therefore they are useless in case you need to do something more advanced using the GStreamer API directly. Hence the need for something new.

My idea with qtvideosink was to implement something that would be a standalone GStreamer element, which would not require the developer to use a specific high level API in order to paint video on QML. In the past I have also written another similar element, qwidgetvideosink, which is basically the same idea, but for QWidgets. After looking at the problem a bit more carefully, I realized that in fact qwidgetvideosink and qtvideosink would share a lot of their internal logic and therefore I could probably do one element generic enough to do both painting on QWidgets and on QML and perhaps more surfaces. And so I did.

I started by taking the code of qtgst-qmlsink, a project that was started by a colleague here at Collabora last year, with basically the same intention, but which was never finished properly. This project was initially based on QtMultimedia’s GStreamer backend. As a first step, I did some major refactoring to clean it up from its QtMultimedia dependencies and to make it an independent GStreamer plugin (as it used to be a library). Then I merged it with qwidgetvideosink, so that they can share the common parts of the code and also wrote a unit test for it. Sadly, the unit test proved something that I was suspecting already: the original QtMultimedia code was quite buggy. But I must say I enjoyed fixing it. It was a good opportunity for me to learn a lot of things on video formats and on OpenGL.

How does it work

First of all, you can create the sink with the standard gst_element_factory_make method (or its equivalent in the various bindings). You will notice that this sink provides two signals, an action signal (a slot in Qt terminology) called “paint” and a normal signal called “update”. “update” is emitted every time the sink needs the surface to be repainted. This is meant to be connected directly to QWidget::update() or QGraphicsItem::update() or something similar. The “paint” slot takes a QPainter pointer and a rectangle (x, y, width, height as qreals) as its arguments and paints the video inside the given rectangle using the given painter. This is meant to be called from the widget’s paint event or the graphics item’s paint() function. So, all you need to do is to take care of those two signals and qtvideosink will do everything else.

Getting OpenGL into the game

You may be wondering how this sink does the actually painting. Using QPainter, using OpenGL or maybe something else? Well, there are actually two¬†variants of this video sink. The first one, qtvideosink,¬†just uses QPainter. It is able to handle only RGB data (only a subset of the formats that QImage supports) and does format conversion and scaling in software. The second one, however, qtglvideosink, uses OpenGL/OpenGLES with shaders. It is able to handle both RGB and YUV formats and does format conversion and scaling in hardware. It is used in exactly the same way as qtvideosink, but it requires a QGLContext pointer to be set on its “glcontext” property before¬†its state is set to READY. This of course means that the underlying surface must support OpenGL (i.e. it must be one of QGLWidget, QGLPixelBuffer or QGLFrameBufferObject). To get this working on QGraphicsView/QML, you just need to set a QGLWidget as the viewport of QGraphicsView and use this widget’s QGLContext in the sink.

qtglvideosink uses either GLSL shaders or ARB fragment program shaders if GLSL is not supported. This means it should work on pretty much every GPU/driver combination that exists for linux on both desktop and emebedded systems. In case no shaders are supported, it will fail to change its state to READY and then you can just substitute it with qtvideosink, which is guaranteed to work on all platforms supported by Qt.

qtglvideosink¬†also has an extra feature: it supports the GstColorBalance interface. Color adjustment is done in the shaders together with the format conversion. qtvideosink doesn’t support this, as it doesn’t make sense. Color adjustment would need to be implemented in software and this can be done better by plugging a videobalance¬†element before the sink. No need to duplicate code.

So, which variant to use?

If you are interested in painting video on QGraphicsView/QML, then qtglvideosink¬†is the best choice of all sinks. And if for any reason the system doesn’t support OpenGL shaders, qtvideosink¬†is the next choice. Now if you intend to paint video on normal QWidgets, it is best to use one of the standard GStreamer sinks for your platform, unless you have a reason not to. QWidgets can be transformed to native system windows by calling their winId() method and therefore any sink that implements the GstXOverlay interface can be embedded in them. On X11 for example, xvimagesink¬†is the best choice. However, if you need to do something more tricky and embedding another window doesn’t suit you very well, you could use qtglvideosink¬†in a QGLWidget (preferrably) or qtvideosink¬†/ qwidgetvideosink¬†on a standard QWidget.

Note that¬†qwidgetvideosink¬†is basically the same thing as qtvideosink, with the difference that it takes a QWidget pointer in its “widget” property and handles everything internally for painting on this widget. It has no signals. Other than that, it still does painting in software with QPainter, just like qtvideosink. This is just there to keep compatibility with code that may already be using it, as it already exists in QtGStreamer 0.10.1.

This is actually 0.10 stuff… What about GStreamer 0.11/1.0?

Well, if you are interested in 0.11, you will be happy to hear that there is already a partial 0.11 port around. Two weeks ago I was at the GStreamer 1.0 hackfest at Malaga, Spain, and one of the things I did there was porting qtvideosink to 0.11. I must say the port was quite easy to do. However, last week I added some more stuff in the 0.10 version that I haven’t ported yet to 0.11. I’ll get to that soon, it shouldn’t take long.

Try it out

The code lives in the qt-gstreamer repository. The actual video sinks are independent from the qt-gstreamer bindings, but qt-gstreamer itself has some helper classes for using them. Firstly there is QGst::Ui::VideoWidget, a QWidget subclass which will accept qtvideosink, qtglvideosink¬†and qwidgetvideosink¬†just like any other video sink and will transparently do all the required work to paint the video in it. Secondly, there is QGst::Ui::GraphicsVideoWidget and QGst::Ui::GraphicsVideoSurface. Those two are meant to be used together to paint video on a QGraphicsView or QML. You can find more about them at the documentation in graphicsvideosurface.h¬†(this will soon be on the documentation website). Finally, there is a QtGStreamer QML plugin, which exports a “VideoItem” element if you “import QtGStreamer 0.10”. This is also documented in the GraphicsVideoSurface header.¬†All of this will soon be released in the upcoming qt-gstreamer 0.10.2.

So, last week we released the first version (technical preview) of Telepathy-KDE along with KDE SC 4.7. The release is separated from the KDE SC (it’s just a technical preview and hasn’t gone through kdereview yet), it just happened to be released at the same time. I would like to thank everyone in the team for making this release possible, after all those years that this project has been sitting there in playground, and especially David and Martin who did most of the hard work lately. If you want to try it, check with your distribution for binary packages or compile it from source¬†(the source can be downloaded from here).

In other news, I am going to the Desktop Summit this year. See you all there:)

Last weekend I went to fosscomm 2011, a Greek conference on Free and Open Source Software, together with my friend Nick Kossifidis (mickflemm), at the University of Patras. I can say we had a wonderful time there. I met many interesting people, some that I knew from the internet already and some that I didn’t, I attended many interesting talks about topics that I had limited or no knowledge and I also took part in fosswar, a wargames competition that had some quite interesting challenges.

Fosswar was very exciting. There were five challenges (you can get them here if you are interested). People were organized in teams, splitting the 5 challenges between them or collaborating on some of them. When it started, there was no room to sit with my laptop, so I stayed for some time trying to help my friend with the challenge that he started solving (challenge 5, reverse engineering). A little later, some people left, so I thought why not start solving challenge 4 (exploitation), which nobody in my friend’s team had started solving. And so I did…

In this challenge, we were given the source code of a C program that had an exploitable security hole that we had to exploit.¬†The program works like this:¬†Initially, it allocates an array of many “struct bogus”, where “struct bogus” is:

struct bogus {
  size_t magic;
  fptr f;
  char buffer[16];
} bogus_t;

This array is dynamically allocated with mmap() on a predefined memory address (0x80000000).¬†After that, it populates the buffers of all the “struct bogus” with the character ‘M’ (0x4D), the magic numbers with ~0 (0xFFFFFFFF on 32-bit and 0xFFFFFFFFFFFFFFFF on 64-bit) and the function pointers (fptr f) with 0.¬†When everything is initialized, it starts reading from stdin and places whatever it reads on a 1KB buffer on the stack. Then, it copies the contents of the buffer to the 16-byte buffer of a random “struct bogus” in the array and then it iterates over all the “struct bogus” in the array, starting from the second one, verifying that their magic number is still ~0 and executing the function f, if the function pointer f is not null.¬†Ok, this is not the most useful program in the world, it is *made* to be exploited, but well, let’s see how this can be done. View full article »

QtGStreamer 0.10.1

This weekend I released QtGStreamer 0.10.1, the first stable version of QtGStreamer. This release marks the beginning of the stable 0.10 series of QtGStreamer that will continue for the lifetime of GStreamer 0.10.¬†For those of you that don’t yet know what QtGStreamer is, it is a set of libraries that provide Qt-style C++ bindings for GStreamer, plus extra helper classes and elements for better integration of GStreamer in Qt applications.

I must say thanks a lot to Mauricio, the co-developer of QtGStreamer, who helped me a lot with the design and code, to the GStreamer community, who accepted this project under the GStreamer umbrella with great enthusiasm, to Nokia for sponsoring it, to Collabora for assigning me and Mauricio to work on it and to all those developers who are already using it in their projects and have helped us by providing feedback.

The future

Development of course does not stop here. It just started. We will try to improve the bindings as much as we can by exporting more and more of GStreamer’s functionality, by adding more and more convenience methods/classes and/or gstreamer elements that ease the use of GStreamer in Qt applications and by collecting opinions and ideas from all of you out there that will use this API. This last bit is quite important imho, so, if you have any suggestions to make about things that you don’t like or things that you would like to see implemented, please file a bug to let us know.

Use in KDE

I am quite happy to see that this library already has early adopters in KDE. Apart of course from my telepathy-kde-call-ui (ex kcall), which is the “father” of QtGStreamer, QtGStreamer is also used in kamoso, a cheese-like camera app, whose authors,¬†Alex Fiestas and¬†Aleix Pol, have been very patient waiting for me to release QtGStreamer before they release kamoso and have also been very supportive during all this time (thanks!).

Personal thoughts

I must say this project was fun to develop. During development, I learned a lot about C++ that I didn’t know before and I also learned how GObject works, which I must say is quite interesting, although ugly for my taste. Learning more about C++ was my main source of interest from the beginning of the project, and for some period of time I couldn’t even imagine that this project would ever reach here, but I kept coding it for myself. Obviously, I am more than happy now that this finally evolved into something that is also useful for others and has wide acceptance:)

What is Telepathy-KDE

There seems to be a lot of confusion about what the Telepathy-KDE project is and what it has to do with Kopete. I’ll try and explain in this blog post everything, so that it is clear to everyone.

First of all, Telepathy is a framework for writing applications that can use real-time communication and collaboration features. In Telepathy, there are the so-called connection managers that connect to IM and similar networks and the clients that use those connections over D-Bus. This allows dividing the several tasks of an IM client to several applications, which makes it easier to reuse code and easier for applications to add collaboration features without caring about protocols, contact lists, presence status and all that stuff.

In Telepathy-KDE what we are trying to do is to integrate Telepathy with the KDE Plasma desktop. What we imagine is not to have a monolithic IM client like kopete or empathy but to integrate all the features of an IM client directly into the desktop. For this reason, we are going to add the following components into the KDE SC:

  1. A presence plasmoid. This will be a plasmoid sitting in your notification area or somewhere else, showing your online status and allowing you with a popup to change status, to enter a status message, etc…
  2. A contact list application. This will be a standalone application that will just show the contact list. It will of course have all the necessary actions to start a chat or a call or do something else with any of your contacts.
  3. A chat window application. This will be a standalone application providing just the chat window. When a new chat starts, it will be auto-launched via D-Bus service activation and allow you to chat.
  4. A VoIP call window application. This will again be a standalone application providing the call window, also auto-launched to handle calls. This is actually KCall, what I wrote in last year’s summer of code, but it won’t have the contact list and won’t be named “KCall”.
  5. An approver daemon. This will be a daemon sitting in the background and listening for incoming channels. When somebody requests that you start doing something with him (be it chat, video call, play a game together, share your desktop, etc…), it will show a KNotify popup allowing you to accept or reject the request.
  6. A file transfer daemon. This will be a daemon that will be auto-launched like the chat and call windows when you want to do a file transfer to or from one of your contacts and handle that file transfer for you.
  7. The nepomuk integration daemon. This is an implementation detail, really internal, not shown to the users. This will allow you to have metacontacts by pushing all of your contacts into the nepomuk database and defining relations between them. It will also allow at some point sharing contacts with akonadi and other cool stuff.

In the future, other components could be added, such as a logger daemon that logs all your chats into files or into a database or something like that and of course it will be very simple to add collaboration features to other applications for doing anything with your contacts. For example, krdc already has telepathy integration and it is possible that if someone requests you over telepathy to share his desktop, you could use krdc to view his desktop, without caring about firewalls or anything. Unfortunately, the server side of this is currently only implemented in gnome, so only a user using gnome can currently share his desktop with you, but that will be fixed in the future.

As a sidenote here, telepathy also allows you to share D-Bus connections over the IM network, which makes it extremely easy to add collaboration features to an application that has no idea about networks or protocols. With this feature, called D-Bus tubes, all you have to do in your application is to expose a D-Bus interface which will be called from the remote side using normal D-Bus calls, as if the other side was running on the same computer. With this feature, we could add collaboration features to many KDE applications in the future very easily. Unfortunately, this currently requires a patch in Qt that has not been merged yet and it is not yet certain if it will make it for Qt 4.8 (which actually screws the whole feature, but we can still hope it will be in Qt 4.8, so that we can start using it in KDE 4.7 or 4.8).

To get to kopete now, as you realize, there is no much place for kopete in all this. So, as soon as we merge all this in the KDE SC, kopete is going to get out of there. All in all, it has not received much development in the last years and even many of its former maintainers are now looking towards Telepathy-KDE, so I don’ t think we have any reason to keep it around. In addition, kopete’s code is not very much reusable in its current form, so we are not going to use it at all. Many people have stated that this may be a bad idea, but we have actually tried to port code from kopete and it didn’t really work, so we decided to do a new implementation from scratch.

I hope that pretty much explains everything now. Let’s stop talking about kopete and let’s start working on Telepathy-KDEūüėÄ

PS: If you want to get involved with it, come and find us on irc in #kde-telepathy on

This weekend I participated in the Telepathy-KDE sprint at Collabora‘s offices in Cambridge. We gathered here to settle things down, make some design decisions, make future plans and start hacking on them. In overall, I think this was quite successful. We now all have a clear plan of what to do and what to aim for in the first release.

Things we did include:

  • We all together discussed the release roadmap. The first release is expected to be around when KDE SC 4.6 will be released, but not as part of KDE SC, since that would require us to merge stuff before the hard feature freeze which is too close and we don’t think we can make it.
  • We all together discussed about the components that we have, what problems each one has, what needs to be done, what are the blocker issues, etc and assigned jobs to everyone.
  • Olli gave talks about telepathy-qt4 and the suggested git workflow that we are going to follow as soon as we migrate to git, which will happen as soon as the KDE admins allow us.
  • Dario, Olli and Andre together hacked on and reviewed the telepathy-qt4 cmake branch, which seems to be in quite a good shape now for upstream inclusion.
  • Olli, Daniele and me discussed about code from our projects that could be upstreamed in telepathy-qt4 and in fact Olli did collect some nice ideas from us.
  • George and Sebastian looked at some nepomuk stuff that needed fixing and fixed them (it’s just nepomuk stuff for me, I have no idea what’s going on on that level yet :P).
  • Andre, Sebastian, Will, Dario and David did some UI mockups on the whiteboard that looked pretty cool.¬†Andre later even did a quick QML mockup of the contact list.
  • Olli, George and me, with some input from Simon McVittie today discussed about how the approver (the thing that pops up asking you if you want to accept or reject a chat or a call or something similar) should be and behave. We will probably have to do some telepathy specification additions for this one, but it’s good that we finally came to a sensible conclusion on a problem that has actually been troubling some of us for a long time.
  • Dominik and David hacked on the chat window, doing some cool things like adding support for loading Adium themes.
  • Lots of other cool stuff, including eating a lot of pizza and burgers, drinking a lot of beer, socializing with the Collabora people, etc…ūüėõ

I think that’s all I had to say for now, stay tuned for more news about Telepathy-KDE:)

PS: We also have a group photo that can be found¬†here, taken by Sjoerd Simons with Daniele’s camera:)

Multimedia sprint

Today is an exciting day. I’m currently at the Athens airport, waiting for my next flight to Munich and then to Geneva, with final destination being Randa, Switzerland, where the kde multimedia & edu sprint will take place the following days. I hope everything is going to be fine. I can’t wait to meet all the other kde people there:)

The reason I’m going to that meeting is that I wish to take part in the phonon/QtMultimedia discussions and also try to find some solution for KCall’s integration with the rest of kde, since it currently uses Gstreamer for some reasons that I won’t repeat againūüėČ I hope that all these discussions will have nice results.


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