Tomorrow I will be heading off to attend the GStreamer Application Porting Hackfest in Malaga, Spain. I think we have managed to pull together an absolutely incredible group of people for this event and I have great hopes that by next weekend we will have squashed a ton of bugs in GStreamer 0.11/1.0 and also have initial ports of a long range of important applications and bindings. This is the first time in GStreamer history that we are trying to hold a hackfest focused on application developers, but hopefully it will be the first of many and that they can become a good way for the core GStreamer community and the application development community to interact and collaborate more closely.
Also want to say a special thanks to the community members attending the event on their own and also to the companies sending their employees to the hackfest; Collabora, Fluendo, Flumotion and Igalia and finally a special thanks to the GNOME Foundation for sponsoring some of the attendees.
Hopefully I will be able to post some screenshots of a fully functional GStreamer 1.0 Transmageddon next weekend
Just posted another interview on the Collabora website, this time with Gustavo Noronha Silva talking about WebKit and some of the work he and Collabora are doing around that project. So be sure to check it out if you want to learn more about things like WebKit and Clutter integration and how WebKit impacts the GNOME platform.
So I did a bit of work last week to convert the Collabora website to HTML5. The actual porting was quite simple, mostly replacing the DOCTYPE tag to the new HTML5 one. Found a few other issues through the W3C validator, but nothing major. Today I took the next (small) step in the process by actual adding some real HTML5 content to the site. Actually I only sort of did. Instead of hosting the video locally and using the new video tag I ended up uploading it to youtube and embedding the WebM video in our page. The small video clip I added is demonstrating the HTML5 video editing demo we released recently. (For those of you who missed it I recommend the HTML5 video editing blog entry by Mateu Batle, which explains the whole thing in detail and also links to the code).
As a sidenote, to make this I actually relied on the GNOME 3 built in screen capture support, which I have to say worked like a charm Always felt screen casting to be a pain before, but this time it worked very well for me.
This time we are talking with Youness Alaoui who is one of the maintainers of Farstream, the audio and video conferencing framework built on top of GStreamer. We also cover another of Youness Alaoui projects, libnice, the NAT traversal library. So if you want to know what is happening with audio and video conferencing on Linux be sure to read the full interview with Youness Alaoui here.
The Ubicast recording system is really impressive (and uses GStreamer :). If you look at the talks they recorded at the GStreamer Conference 2011 you can get an impression of how nice their system is, capturing both the slides and the speakers with a high resolution camera and automatically cropping and mixing them together. A big thanks to Florent and Anthony for their hard work during the conference.
Had an absolute blast and I am really happy the GStreamer Conference again turned out to be a big success. A big thanks to the platinum sponsor Collabora, and the two silver sponsors Fluendo and Google who made it all possible. Also a big thanks to Ubicast who was there onsite recording all talks. They aim to have all the talks online within a Month.
While I had to run a bit back and forth to make sure things was running smoothly, I did get to some very interesting talks, like Monty Montgomery from Xiph.org talking about the new Opus audio codec they are working on with the IETF and the strategies they are working on to fend of bogus patent claims.
On a related note I saw that Apple released their lossless audio codec ALAC as free software under the Apache license. Always nice to see such things even if ALAC for the most part has failed to make any headway against the already free FLAC codec. If Apple now would join the effort around WebM things would really start looking great in the codec space.
We did a Collabora booth during the LinuxCon and Embedded Linux days that followed the GStreamer Conference. Our demos showcasing a HTML5 video editing UI using GStreamer and the GStreamer Editing Services and video conferencing using Telepathy through HTML5 was a great success and our big screen TV running the Media Explorer media center combined with Telepathy based video conferencing provided us with a steady stream of people to our booth. For those who missed the conference all the tech demos can be grabbed from this Prague-demo Ubuntu PPA.
So as you might imagine I was quite tired by the time Friday was almost done, but thanks to Tim Bird and Sony I got a really nice end to the week as I won a Sony Tablet S through the Elinux Wiki editing competition. The tablet is really nice and it was the first tablet I ever wanted, so winning one was really great. The feature set is really nice with built in DLNA support, it can function as a TV remote and it has support for certain Playstation 1 titles. The ‘folded magazine’ shape makes it really nice to hold and I am going to try to use it as an e-book reader as I fly off to Lahore tomorrow morning for my sister-in-laws wedding.
I am really excited about this years GStreamer Conference as we have a lot of ongoing efforts about to come to fruits. From Collabora we got Wim Taymans will be talking about GStreamer 1.0 effort, which we expect to have out before years end and Tim-Philipp Müller will speak about a lot of the other incredible advances we made over the last year. Being in the middle of it I think its easy to go a bit blind due to the gradual process, but things like the new parsing libraries that Thibault Saunier have been working on, which will enable much quicker and better support for things like libva and vdpau plugins in GStreamer. Or the new baseclasses that Mark Nauwelaerts have ported most of our plugins over to now, which in one fell swoop improved our plugin quality by leaps and bounds. And of course there are things like the GStreamer Editing services (GES), discoverer and encodebin which Edward Hervey created, which will make applications like Transmageddon video transcoder and remuxer and the PiTiVi video editor a lot easier to develop.
We will also be doing some real cool demonstrations of stuff we have been working on at Collabora at the Linux Con Showcase on Thursday. Thanks to GES we have a great demo of a mobile editing solution using either QML or HTML5. We have HTML5 video calling using Telepathy and we have Video calling using Telepathy from the Media explorer media center solution.
Another talk that I will be sure not to miss is Jan Schmidt who will be talking about Blu-Ray playback with GStreamer. In addition to being technically interesting Jans talks are always fun, like last year he did his presentation using GStreamer instead of something like LibreOffice, having created his slides as a DVD menu through a small program he wrote to turn SVG files into DVD menus
I have wanted to write about programming with GStreamer and Python for a while. Jono Bacon wrote a nice introduction to GStreamer and Python a long time ago, but I want to share with you some specific tips.
At Collabora we work a lot with GStreamer including helping train developers at our customers to be better at GStreamer development. Being the lowly marketing guy at the company I don’t have the programming chops to teach the hard stuff, but I figured I should be able to put together a very simple article which explains some basics and shows of a little GStreamer development trick I have used to great success in Transmageddon.
Part of what triggered getting this little tutorial done was that I am looking into porting Transmageddon to GTK3 after its next release of Transmageddon. To understand how to write a GTK 3 Python application, using the introspection bindings, I decided a good learning tool for myself would be to try to port the 0.0.1 version of Transmageddon. This version was never released, in fact it was me trying to figure out the very basics of programming with GTK+ and GStreamer in Python.
The application litterally consists of a GTK+ UI with two buttons. One is a ‘transcode’ button which when pressed starts a GStreamer transcoding pipeline. The other is my little secret trick, called ‘Debug’. It will when pressed generate a png of the pipeline being run, or not being run for that matter. It has helped me solve a ton of bugs and issues in Transmageddon since I started the project and hopefully it can be a useful trick for you too.
You can find a tarball here with the code below, the .ui file from Glade and a which.py file (which.py is a python version of the Unix which tool, which I found online).
First let me give you the code of the application, I tried to annotate the code in detail to make it easy to follow, even if you haven’t played with either GTK3 or GStreamer before.
# Simple example GTK3 + GStreamer 0.10.x Application for transcoding
# GTK3 using gobject introspection for bindings, GStreamer using manual bindings
# Also includes how to set up dotfile generation
# Setting GST_DEBUG_DUMP_DOT_DIR environment variable enables us to have a dotfile generated
os.environ["GST_DEBUG_DUMP_DOT_DIR"] = "/tmp"
from gi.repository import Gtk
# creating a basic transcoder class
self.pipeline = gst.Pipeline("TranscodingPipeline") # creating overall pipeline object
# Creating GStreamer filesrc element and sets it to read a specific mp3 file
self.filesrc = gst.element_factory_make("filesrc", "filesrc")
self.pipeline.add(self.filesrc) # add this first plugin to the pipeline object
# Use highlevel decodebin2 element to choose which GStreamer elments to use
# for decoding automatically
self.decoder = gst.element_factory_make("decodebin2", "decoder")
# Connect to signal that will let us know that decodebin2 got a pad we can connect
# to which has the decoded media file on it
# create an audioconvert element to convert bitrate if needed
self.audioconverter = gst.element_factory_make("audioconvert", "audioconverter")
# create audioencoder, in this case the Vorbis encoder
self.audioencoder = gst.element_factory_make("vorbisenc", "audioencoder")
# create ogg muxer to hold vorbis audio
self.oggmuxer = gst.element_factory_make("oggmux", "oggmuxer")
# create file output element to write new file to disk
self.filesink = gst.element_factory_make("filesink", "filesink")
# Now that all elements for the pipeline are create we link them together
# set pipeline to playing which means all the connected elements in the pipeline
# starts pushing data to each other
# create a simple function that is run when decodebin gives us the signal to let us
# know it got audio data for us. Use the get_pad call on the previously
#created audioconverter element asking to a "sink" pad.
def OnDynamicPad(self, dbin, pad, islast):
# extremely simple UI using a GtkBuilder UI generated with Glade, just two buttons.
# One to start transcode and one to run pipeline debug
self.builder = Gtk.Builder()
self.uifile = "supersimple-gtk3.ui"
self.window = self.builder.get_object ("MainWindow")
self.window.connect ("destroy", self.dialog_destroyed) # this allows the application
# to be cleanly killed
# Call the two buttons in the UI
self.transcodebutton = self.builder.get_object("transcodebutton")
self.debugbutton = self.builder.get_object("debugbutton")
# Connect to the clicked signal on both buttons
self.transcodebutton.connect ("clicked", self.on_TranscodeButton_clicked)
self.debugbutton.connect ("clicked", self.on_debug_activate)
# set window size to avoid it being so small it gets lost on the desktop
self.window.set_default_size (580, 435)
def on_TranscodeButton_clicked(self, widget):
self._transcoder = Transcoder()
def dialog_destroyed (self, dialog):
# this function generates the dot file, checks that graphviz in installed and
# then finally generates a png file, which it then displays
def on_debug_activate(self, widget):
dotfile = "/tmp/supersimple-debug-graph.dot"
pngfile = "/tmp/supersimple-pipeline.png"
if os.access(dotfile, os.F_OK):
if os.access(pngfile, os.F_OK):
gst.DEBUG_BIN_TO_DOT_FILE (self._transcoder.pipeline, \
# check if graphviz is installed with a simple test
dot = which.which("dot")
os.system(dot + " -Tpng -o " + pngfile + " " + dotfile)
Gtk.show_uri(None, "file://"+pngfile, 0)
print "The debug feature requires graphviz (dot) to be installed."
print "Transmageddon can not find the (dot) binary."
if __name__ == "__main__":
hwg = SuperSimpleUI()
The first thing happening in the file after importing the basis system classes and the which.py tool, is that we set the ‘GST_DEBUG_DUMP_DOT_DIR’ environment variable. When you set this value, GStreamer will be able to at any time dump the pipeline and elements to a ‘dot’ file, which can be turned into a nice looking png by the graphviz command line tool (should be available in most distributions).
Next I import GTK and GStreamer, as you see I don’t yet use the gobject introspection version of GStreamer as that is not fully working yet, but I plan to try to port this simple application to GStreamer 1.0, in which gobject introspection will be the supported way of using Python.
Next is setting up the GStreamer pipeline. You always start by creating a pipeline object, consider this the canvas onto which you will paint the GStreamer streaming pipelines. The next step is to assemble all the GStreamer plugins we want to use in the application. First I create a filesrc object pointing to the file I want to transcode, be sure to point that to a file of your own if trying this application. Next is creating the decodebin2 element. Decodebin2 is one of a set of high level elements in GStreamer, called bins, which contains a wide range of plugins inside. These high level elements are there to make things a lot simpler, and in the case of decodebin2 it will automatically put together the plugins needed to convert your incoming file to raw audio and video (or just demux the file). This means your input doesn’t need to be a mp3 file, like I used, as decodebin2 will reconfigure itself to handle any file you throw at it. After this I create a series of elements to enable me to encode the data into a Ogg Vorbis file. I am doing that to help explain how elements are stringed together, but there is another high level element, encodebin, which I could have used instead. Transmageddon uses encodebin in its git version.
Once all the elements are created you can think of them as boxes spread around on your pipeline canvas, but in order for GStreamer to know how you want to connect them together you need to link them together, as you can see I do with statements like ‘self.filesrc.link(self.decoder)’, which connects the filesrc element I created with the decoder element.
The one special element here is decodebin, which being a dynamic element I need to link it once the pad found signal is fired. Also to link I need to request a compatible pad from the element I am linking with, in this case the audioconverter element.
The last part of the GStreamer setup is setting the pipeline to playing state, which is the state where the pipeline is running. While not a big concern in this very simple application, dealing with state changes in GStreamer is going to be one of the major items you look out for. The GStreamer plugin writers guide contains a chapter discussing the basics of the four states "NULL", "READY", "PAUSED" and "PLAYING". Your pipeline (and all elements) always start at Null state and will go through each of the other stanges to reach Playing. So while we only set state to PLAYING in this simple application, GStreamer will in the background go through READY and PAUSED. The reason the intermediary states matter is because certain things happen at each, so for instance if you want to do some analysis of a file before starting to run your pipeline fully you want to be in PAUSED state as GStreamer will then start pulling the initial data through the pipeline and thus allow you to get information from your elements about the stream or file. One important thing to keep in mind as you develop more advanced applications is that the individual elements can have a different state than the pipeline, but when the state of the pipeline changes it will change the state of the plugins along with it, so you never want your pipeline to be more than one level lower than any of your elements, as that will cause the element to jump down to that state and thus lose the negotiation and information it had assembled.
I am not going to go into a lot of detail about the GUI, it is a very simple GTK user interface built using Glade, and hooked up using the GTK3 gobject introspection bindings. If you got any questions about it post a comment and I be happy to talk about it. What I want to talk about instead is the on_debug_activate function. I wrote this for Transmageddon, but my hope is that it will be useful for anyone writing a Python application with GStreamer (and I guess it shouldn’t be to hard to port to another language). It will allow you to add a menu entry or button in your application that outputs a png file, like the one you see below, which gives you a nice full view of the pipeline used by GStreamer. Especially if you use things like decodebin2 and encodebin, or have a lot of code dynamically adding/removing elements, it can be really useful to see what pipeline ended up being used. And if you have elements that you created, but forgot to link inn, they will appear as orphaned boxes in the file, allowing you to detect such issues. The important thing to remember is that it needs the graphwiz application to be installed on your system and available in the executable path.
Anyway, I hope this has been useful and I plan to post and updated version of this simple application, ported to use encodebin and GStreamer 1.0.
Another talk I am especially excited about is the talk by Joshua Doe and Stephen Burks who works for the US Army RDECOM CERDEC NVESD unit(just rolls of the tongue doesn’t it :). Who will talk about their use of GStreamer. I know that there are quite a few cases in the military world where GStreamer is used, so I think this talk can be an interesting window into that world, which due to its high security nature often can be quite low profile even when things are not directly secret.
A big thanks you to our sponsors this year Collabora, Fluendo, Google and UbiCast. Without their support it would not have been possible to put this event together.
Make sure to register for this years GStreamer Conference before the 24th of September in order to get the early bird fee. Looking forward to seeing you all there!
And if you are still not 100% sure you will attend, make sure to look at the schedule and speakers overview, because I am sure they will convince you to come
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