Über latest Media Source Extensions improvements in WebKit with GStreamer

In this post I am going to talk about the implementation of the Media Source Extensions (known as MSE) in the WebKit ports that use GStreamer. These ports are WebKitGTK+, WebKitEFL and WebKitForWayland, though only the latter has the latest work-in-progress implementation. Of course we hope to upstream WebKitForWayland soon and with it, this backend for MSE and the one for EME.

My colleague Enrique at Igalia wrote a post about this about a week ago. I recommend you read it before continuing with mine to understand the general picture and the some of the issues that I managed to fix on that implementation. Come on, go and read it, I’ll wait.

One of the challenges here is something a bit unnatural in the GStreamer world. We have to process the stream information and then make some metadata available to the JavaScript app before playing instead of just pushing everything to a playing pipeline and being happy. For this we created the AppendPipeline, which processes the data and extracts that information and keeps it under control for the playback later.

The idea of the our AppendPipeline is to put a data stream into it and get it processed at the other side. It has an appsrc, a demuxer (qtdemux currently) and an appsink to pick up the processed data. Something tricky of the spec is that when you append data into the SourceBuffer, that operation has to block it and prevent with errors any other append operation while the current is ongoing, and when it finishes, signal it. Our main issue with this is that the the appends can contain any amount of data from headers and buffers to only headers or just partial headers. Basically, the information can be partial.

First I’ll present again Enrique’s AppendPipeline internal state diagram:

First let me explain the easiest case, which is headers and buffers being appended. As soon as the process is triggered, we move from Not started to Ongoing, then as the headers are processed we get the pads at the demuxer and begin to receive buffers, which makes us move to Sampling. Then we have to detect that the operation has ended and move to Last sample and then again to Not started. If we have received only headers we will not move to Sampling cause we will not receive any buffers but we still have to detect this situation and be able to move to Data starve and then again to Not started.

Our first approach was using two different timeouts, one to detect that we should move from Ongoing to Data starve if we did not receive any buffer and another to move from Sampling to Last sample if we stopped receiving buffers. This solution worked but it was a bit racy and we tried to find a less error prone solution.

We tried then to use custom downstream events injected from the source and at the moment they were received at the sink we could move from Sampling to Last sample or if only headers were injected, the pads were created and we could move from Ongoing to Data starve. It took some time and several iterations to fine tune this but we managed to solve almost all cases but one, which was receiving only partial headers and no buffers.

If the demuxer received partial headers and no buffers it stalled and we were not receiving any pads or any event at the output so we could not tell when the append operation had ended. Tim-Philipp gave me the idea of using the need-data signal on the source that would be fired when the demuxer ran out of useful data. I realized then that the events were not needed anymore and that we could handle all with that signal.

The need-signal is fired sometimes when the pipeline is linked and also when the the demuxer finishes processing data, regardless the stream contains partial headers, complete headers or headers and buffers. It works perfectly once we are able to disregard that first signal we receive sometimes. To solve that we just ensure that at least one buffer left the appsrc with a pad probe so if we receive the signal before any buffer was detected at the probe, it shall be disregarded to consider that the append has finished. Otherwise, if we have seen already a buffer at the probe we can consider already than any need-data signal means that the processing has ended and we can tell the JavaScript app that the append process has ended.

Both need-data signal and probe information come in GStreamer internal threads so we could use mutexes to overcome any race conditions. We thought though that deferring the operations to the main thread through the pipeline bus was a better idea that would create less issues with race conditions or deadlocks.

To finish I prefer to give some good news about performance. We use mainly the YouTube conformance tests to ensure our implementation works and I can proudly say that these changes reduced the time of execution in half!

That’s all folks!

Web Engines Hackfest according to me

And once again, in December we celebrated the hackfest. This year happened between Dec 7-9 at the Igalia premises and the scope was much broader than WebKitGTK+, that’s why it was renamed as Web Engines Hackfest. We wanted to gather people working on all open source web engines and we succeeded as we had people working on WebKit, Chromium/Blink and Servo.

The edition before this I was working with Youenn Fablet (from Canon) on the Streams API implementation in WebKit and we spent our time on the same thing again. We have to say that things are much more mature now. During the hackfest we spent our time in fixing the JavaScriptCore built-ins inside WebCore and we advanced on the automatic importation of the specification web platform tests, which are based on our prior test implementation. Since now they are managed there, it does not make sense to maintain them inside WebKit too, we just import them. I must say that our implementation is fairly complete since we support the current version of the spec and have almost all tests passing, including ReadableStream, WritableStream and the built-in strategy classes. What is missing now is making Streams work together with other APIs, such as Media Source Extensions, Fetch or XMLHttpRequest.

There were some talks during the hackfest and we did not want to be less, so we had our own about Streams. You can enjoy it here:

You can see all hackfest talks in this YouTube playlist. The ones I liked most were the ones by Michael Catanzaro about HTTP security, which is always interesting given the current clumsy political movements against cryptography and the one by Dominik Röttsches about font rendering. It is really amazing what a browser has to do just to get some letters painted on the screen (and look good).

As usual, the environment was amazing and we had a great time, including the traditional Street Fighter‘s match, where Gustavo found a worthy challenger in Changseok 🙂

Of course, I would like to thank Collabora and Igalia for sponsoring the event!

And by the way, quite shortly after that, I became a WebKit reviewer!

WebKit Contributors Meeting 2015 (late, I know)

After writing my last post I realized that I needed to write a bit more about what I had been doing at the WebKit Contributors Meeting.

First thing to say is that it happened in March at Apple campus in Cupertino and I atteded as part of the Igalia gang.

My goal when I went there was to discuss with Youenn Fablet about Streams API and we are implementing and see how we could bootstrap the reviews and being to get the code reviewed and landed efficiently. Youenn and I also made a presentation (mainly him) about it. At that moment we got some comments and help from Benjamin Poulain and nowadays we are also working with Darin Adler and Geoffrey Garen so the work is ongoing.

WebRTC was also a hot topic and we talked a bit about how to deal with the promises as they seem to be involved in the WebRTC standard was well. My Igalian partner Philippe was missed in this regard as he is involved in the development of WebRTC in WebKit, but he unfortunately couldn’t make it because of personal reasons.

I also had an interesting talk with Jer Noble and Eric Carlson about Media Source and Encrypted Media Extensions. I told them about the several downstream implementations that we are or were working on, specially the WebKit4Wayland one and that we expect to begin to upstream soon. They commented that they still have doubts about the abstractions they made for them and of course I promised to get back to them when we begin with the job. Actually I already discussed some issues with Quique, another fellow Igalian.

Among the other interesting discussions, I found very necessary the migration of Mac port to CMake. Actually, I am experiencing now the painbenefits of using XCode to add files, specially the generated ones to the compilation. I hope that Alex succeeds with the task and soon we have a common build system for all main ports.

ReadableStream almost ready

Hello dear readers! Long time no see! You might thing that I have been lazy, and I was in blog posting but I was coding like mad.

First remarkable thing is that I attended the WebKit Contributors Meeting that happened in March at Apple campus in Cupertino as part of the Igalia gang. There we discussed of course about Streams API, its state and different implementation possibilities. Another very interesting point which would make me very happy would be the movement of Mac to CMake.

In a previous post I already introduced the concepts of the Streams API and some of its possible use cases so I’ll save you that part now. The news is that ReadableStream has its basic funcionality complete. And what does it mean? It means that you can create a ReadableStream by providing the constructor with the underlying source and the strategy objects and read from it with its reader and all the internal mechanisms of backpresure and so on will work according to the spec. Yay!

Nevertheless, there’s still quite some work to do to complete the implementation of Streams API, like the implementation of byte streams, writable and transform streams, piping operations and built-in strategies (which is what I am on right now).I don’t know either when Streams API will be activated by default in the next builds of Safari, WebKitGTK+ or WebKit for Wayland, but we’ll make it at some point!

Code suffered already lots of changes because we were still figuring out which architecture was the best and Youenn did an awesome job in refactoring some things and providing support for promises in the bindings to make the implementation of ReadableStream more straitghforward and less “custom”.

Implementation could still suffer quite some important changes as, as part of my work implementing the strategies, some reviewers raised their concerns of having Streams API implemented inside WebCore in terms of IDL interfaces. I have already a proof of concept of CountQueuingStrategy and ByteLengthQueuingStrategy implemented inside JavaScriptCore, even a case where we use built-in JavaScript functions, which might help to keep closer to the spec if we can just include JavaScript code directly. We’ll see how we end up!

Last and not least I would like to thank Igalia for sponsoring me to attend the WebKit Contributors Meeting in Cupertino and also Adenilson for being so nice and taking us to very nice places for dinner and drinks that we wouldn’t be able to find ourselves (I owe you, promise to return the favor at the Web Engines Hackfest). It was also really nice to have the oportunity of quickly visiting New York City for some hours because of the long connection there which usually would be a PITA, but it was very enjoyable this time.

Streams API in WebKit at the Web Engines Hackfest

Yes, I know, I should have written this post before you know, blah, blah, excuse 1, blah, excuse 2, etc. 😉

First of course I would like to thank Igalia for allowing me to use the company time to attend the hackfest and meeting such a group of amazing programmers! It was quite intense and I tried to give my best though for different reasons (coordination, personal and so on) I missed some session.

My purpose at the hackfest was to work with Youenn Fablet from Canon on implementing the Streams API in WebKit. When we began to work together in November, Youenn had already a prototype working with some tests, so the idea was taking that, completing, polishing and shipping it. Easy, huh? Not so…

What is Streams? As you can read in the spec, the idea is to create a way of handling different kind of streams with a common high level API. Those streams can be a mapping of low level I/O system operations or can be easily created from JavaScript.

Fancy things you can do:

  • Create readable/writable streams mapping different operations
  • Read/write data from/to the streams
  • Pipe data between different streams
  • Handle backpressure (controlling the data flow) automagically
  • Handle chunks as the web application sees fit, including different data types
  • Implement custom loaders to feed different HTML tags (images, multimedia, etc.)
  • Map some existing APIs to Streams. XMLHttpRequest would be a wonderful first step.

First thing we did after the prototype was defining a roadmap:

  • General ReadableStream that you can create at JavaScript and read from it
  • XMLHttpRequest integration
  • Loaders for some HTML tags
  • WritableStream
  • Piping operations

As you can see in bugzilla we are close to finishing the first point, which took quite a lot of effort because it required:

  • Code cleaning
  • Making it build in debug
  • Improving the tests
  • Writing the promises based constructor
  • Fixing a lot of bugs

Of course we didn’t do all this at the hackfest, only Chuck Norris would have been able to do that. The hackfest provided the oportunity of meeting Youenn in person, working side by side and discussing different problems and possible strategies to solve them, like for example, the error management, queueing chunks and handling their size, etc. which are not trivial given the complexity created by the flexibility of the API.

After the hackfest we continued working and, as I said before, the result you can find at bugzilla. We hope to be able to land this soon and continue working on the topic within the current roadmap.

To close the topic about the hackfest, it was a pleasure to work with such amount of awesome web engines hackers and I would like to finish thanking the sponsors Collabora and Adobe and specially my employer, Igalia, that was sponsor and host.

New media controls in WebKitGtk+ (reloaded)

In December we organized in A Coruña the WebKitGTK+ hackfest at the Igalia premises as usual and also as usual it was an awesome oportunity to meet the rest of the team. For more information about the progress done in the hackfest, you can have a look at KaL’s post.

As part of the hackfest I decided to take a task that it would take some time so that I could focus and I decided to go for rewriting once again the WebKitGTK+ multimedia controls. People who just read this post will wonder why I say again and the reason is that last year we completely redesigned the multimedia controls. This time I have not redesigned them (well, a bit) but rewritten them in JavaScript as the Apple guys had done before.

To get the job done, the first step was bundling the JavaScript code and activating the codepath to use those controls. I used the Apple controls as template so you can imagine that the first result was a non-working monster that at some point reminded to Safari multimedia controls. At that point I could do two things, forking or inheriting. I decided to go with inheritance because it keeps the spirit of WebKit (and almost all Free Software projects) of sharing as much code as possible and because forking later is easier than merging. Then step by step I kept redefining JavaScript methods and tweaking some stuff in the C++ and CSS code to create the current user experience that we had so far.

Some of the non-aesthetic changes are the following:

  • Focus rings are now managed from CSS instead of C++.
  • Tests got new fixes, rebaselines and more love.
  • CMake support for the new controls.
  • Load captions icon from theme.
  • Load and hide elements handled now with CSS (and JavaScript).

The captions icon problem was interesting because I found out that the one we were using was “user-invisible-symbolic” and it was hardcoded directly in the CSS code. I changed it to be loaded from the theme but it raised the issue of using the incorrect metaphor though the current icon looks nice for captions. I filed a GNOME bug (and another WebKit bug to follow this up) so that a new icon can be created for captions/subtitles with the correct metaphor.

And which are the controls aesthetic changes?

  • Show a very subtle gradient when the elements are focused or active to improve the accessibility support (which won’t be complete until bug 117857 is fixed).
  • Volume slider rolls up and down with a nice animation.
  • Some other elements are not shown when they are not needed.
  • Captions menu shows up with both click and mouse hover for coherence with the volume slider.
  • Captions menu is also animated the same way as the volume slider.
  • Captions menu was propertly centered.
  • Captions menu style was changed to make it more similar to the rest of the controls (fonts, margings…)
  • Volume slider shows below the media element when it is too close to the page top and it cannot be shown on it. This was a regression that I introduced with the first rewrite, happy to have it fixed now.

As I already said the aesthetic differences with the former C++ are not a big deal unless you compare them with the original controls:

Starting point

To appreciate the new controls I cannot just show a screenshot, because the nicest thing are the animations. Therefore a video is needed (and if you have WebKit compiled you can experience them yourself)):

Of course, I thank our hackfest sponsors as the it was possible because of them:

Igalia GNOME Foundation

GUADEC 2013 is over

I departed from A Coruña, flying to Barcelona (where I had time to have a coffee with a friend), then to Vienna and then to Brno by bus. It was a bit tiring so after having a quick drink at our hotel with the rest of the Igalians, I just went to bed.

Web, the future is now by my Igalian friend Claudio Saavedra (different from Garnacho) was my first talk (apart from the keynote). Even after knowing the content already, I found quite interesting the way Claudio spoke about the latest changes in the development of Web (a.k.a. Epiphany), specially the way WebKit 2 helps to provide a much better user experience.

I liked a lot Alex Larsson’s talk of High resolution display support in GNOME. His approach of the abstract pixels and all the way down in the stack from Gtk+ was very interesting.

Matt Dalio and his Endless Mobile project just rock, not only because of the tech and GNOME involved but also because of its social implications. Keep going!

Given the rest of my career and my work in WebKit, specially in the WebKitGTK+ port, I am always interested in GStreamer, as it is the framework we use use for multimedia playback (and other ports like EFL and Qt in Linux). What’s cooking in GStreamer talk by Sebastian Dröge and Tim-Philipp Müller was of course mandatory and worth going.

Jan-Christoph Borchardt’s talk about GNOME and ownCloud: desktop plus web for a holisic experience showed everything that is and is coming with ownCloud. I introduced him to Claudio as he mentioned that he would like to see at least Ephy’s bookmarks syncronized with ownCloud. It looks interesting.

I missed Philip Withnall’s talk about Testing online services because it was at the same time as the ownCloud one, but I was interested because of my wife‘s research project about the same subject. Philip, if you read this, leave me a comment or get in touch directly with her as she was very interested.

It is always refreshing to attend Marina Zhurakhinskaya’s talk about Outreach Program for Women: a lesson in collaboration, because I think it is very important to keep reminding ourselves about the relevance of programs to integrate more women into our community and I think we, and specially Marina and the OPW program, get always awesome results, though we cannot fall asleep and keep pushing till, at least, the 50%.

My Igalian friend Juan Suárez had a talk called Writing multimedia applications with Grilo where he showed the easy but powerful possibilities of the Grilo API and its plugins. There was also a lightning talk by an intern about adding support to build Lua plugins for Grilo.

Juan Pablo Ugarte was showing off his Glade skills in his talk about Rich custom user interfaces with Glade and CSS. His slides were made with Glade. Cool!

More secure with less “security” by Stef Walter had a lot of interesting ideas about how to improve security and making at the same time the user’s life easier.

Just after lunch it was the turn of my Igalian friend Martin Robinson who gave the talk about Webkit2 and you and explained many things about the WebKit 2 model, like for example all its layers and how the processes work.

There was another talk given by other fellow Igalians, Alejandro Piñeiro and Joanmarie Diggs, called Tag, your PDF is it that I couldn’t attend. In that case I preferred to prioritize other talks as I can always easily talk to them.

The rest of the talks I attended were:

Of course it would not be a GUADEC without hanging out with friends at the different parties, one of them sponsored by Igalia and Red Hat.

I really enjoyed the tour at the city, which is very beatiful and peaceful, though we had to finish it prematurely because of the impresive storm. On our way back from our unofficial GNOME Hispano dinner, which of course was great, to our hotel, we could see some broken tree branches and even what we think that were some fallen young trees.

The venue was really a nice place (with funny chairs) and the volunteers did an awesome job (THANKS!). Of course, there are always issues, like the AC problem (these things can always happen) and the internet connection which is an inherent problem to almost every GUADEC.

Wonderful work also of Ana, taking a lot of cool pictures, even from me, that you can see in her Flickr collections.

Of course, I cannot forget to thank Igalia for sponsoring my trip.

Strasbourg, there we go!

New media controls in WebKitGtk+

So it looks like my patch for the rework of the WebKitGtk+ media controls was finally landed.

First I would like to thank Igalia for giving me some time to complete this task, which took some work and began at WebKitGtk+ hackfest some time ago with Žan Doberšek and Jon McCann.

Starting point was:

Starting point

As you can see the controls look like an old Gtk+ application without any theming. Jon suggested that we could began with mimicing Chromium controls as they look closer to any modern themed GNOME application and adapt them to use the GNOME symbolic icons and keep some other stuff like the volume bar, but of course making it look nicer.

What was done:

  • Adding the GNOME symbolic icon theme and a method to replace the normal stock icons, though we keep them as fallback.
  • Deep adaptation of Chromium CSS and C++ code to make it suit the GNOME requirements.
  • Some buttons fell off the design, like seeking backwards and forward.
  • Aligned the elements with the pixel ruler to make them as close to perfect as possible in all conditions (as some buttons are hidden in certain situations, like fullscreen, volume…).
  • Fixed a bug about the buffering ranges that was in trunk at that point, but was independent of the code I was cooking.
  • Removed as much of the C++ code as possible to deviate the drawing to CSS, which is more maintainable for design purposes. The only things that are still painted with C++ code are the slider tracks, which depend on parameters than cannot be specified in CSS, like the buffering ranges and the volume (which was not before, but I introduced for design coherence).
  • Removed the focus ring which was making the controls uglier.
  • Removed the dead code.
  • New baselines for the tests, including the pixel ones. Flagged also some tests that are (and will) not working in Chromium either.

I had a small issue with a Chromium guy landing a patch that forced me to change the display of some components from -webkit-box to -webkit-flex and of course, rebasing all related tests. This created a small delay in landing the patch, but it finally did as 143463.

And the result is the following:
New media controls

I don’t know about you guys, but I like it!

GUADEC 2012: state of calvaris

GUADEC 2012 A Coruña

Executive summary

Tired as hell but with my hacking batteries completelly full.

Organization

There was always something to do here and there, which I needed to help with, but I think the most important things that I did were:

  • Organizing the Lightning Talks session, I guess you all remember the sound of the sea and the seaguls that I choose to indicate people that they were running out of time.
  • I helped Marina and Christophe in organizing the Interns’ Lightning Talks, which you can also guess because Marina liked the sea sound and decided to use it also for their session.
  • I helped Juanjo in organizing the BoFs. He planned them and I managed them at the indico.
  • Random stuff
  • Keeping hackers happy. Having Zeenix at my place implied hanging out almost every day with the hackers for dinner and beers so I needed to do my best to have them properly fed and with the deserved ‘party level’. I took some people to do some sightseeing and to several restaurants like A Roda, O Galiñeiro… I even remember going to a place with live music at Os Maios close to a Pulpeira de Arzúa.

The only bad thing I can think of is that I missed some talks because of having a lot of things to do.

Interesting talks

I attended all the talks I could and just tried to avoid the ones by Igalians because for obvious reasons I already knew what they were about, so I’ll mention the ones that I liked most:

  • Jacob Appelbaum’s keynote: Personal data exposure is underestimated by most people but it is something very important that we should care about. It would be interesting to have Tor integrated with GNOME.
  • Every detail matters by Allan: Suddenly you realize that you are in a better mood when using your GNOME 3 and the reason is because there are some guys focusing on having the small bugs fixed that were annoying you without noticing.
  • MinGW-w64 by Marc-André: Quite interesting talk about tools and recipes to crosscompile your programs for the Evil. This is quite important to help us with the task of showing that the GNOME world is as multiplatform as other options (you would be a fool if you think that you can have everything working like a charm on the Evil when using some frameworks that claim to be multiplatform just out of the box).
  • i18n by Gil: Random though: No native English speaker developer was on that talk. We really need to improve this. Then we can talk about tools and other stuff. Though I did not attend the BoF, I talked to Fran Diéguez and my wife Laura about some stuff the students of the Universidade da Coruña could help with to improve translators’ lives, maybe combined with GSoC or OPW.
  • GStreamer talk by Tim Müller: Can’t ever miss it. 1.0 is almost there and it shines!
  • PiTiVi by Jeff: Constant lol. Cannot wait to see the videos uploaded. Really enjoyed it not only because of it being fun, but because of all the new features coming to our favorite video editor.
  • Defensive publications: Patents suck in all senses and even more at FLOSS. These guys should be keynoters at all FLOSS events all over the world, because something I learned lately is that people can do things when they unite. If we help with bringing things to the public knowledge before they are patented by others (because Patent Offices workers are far from perfection considering their model that I do not agree with) we can do something. I recommend you to have a look at the Open Innovation Network.
  • History of GNOME: it is always interesting to look back to see how much we have walked.

Fixed bugs

  • After speaking to Matthias Clasen, I got the permission to apply the patches I had submitted for GB#613595. This was quite an old bug that I had worked on from the times of Hildon in Fremantle. Just after pushing I realized that I had caused a small regression but fortunately I fixed it before having consequences.
  • Bastien closed FDB#49945 about GeoClue by pushing my patch.
  • Edward promised to have a look at the patches I submitted for GB#663869. This is not closed yet, but I hope he does not forget 😉

Thanks

And of course, I need to thank Igalia for sponsoring me by attending and helping at GUADEC:

Igalia