Arun Raghavan

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Year: 2014

Notes from the PulseAudio Mini Summit 2014

The third week of October was quite action-packed, with a whole bunch of conferences happening in Düsseldorf. The Linux audio developer community as well as the PulseAudio developers each had a whole day of discussions related to a wide range of topics. I’ll be summarising the events of the PulseAudio mini summit day here. The discussion was split into two parts, the first half of the day with just the current core developers and the latter half with members of the community participating as well.

I’d like to thank the Linux Foundation for sparing us a room to carry out these discussions — it’s fantastic that we are able to colocate such meetings with a bunch of other conferences, making it much easier than it would otherwise be for all of us to converge to a single place, hash out ideas, and generally have a good time in real life as well!

Incontrovertible proof that all our users are happy

Happy faces — incontrovertible proof that everyone loves PulseAudio!

With a whole day of discussions, this is clearly going to be a long post, so you might want to grab a coffee now. :)

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Quick-start guide to gst-uninstalled for GStreamer 1.x

Update: gst-build is the current way to build GStreamer for developement. I’m leaving the post up for posterity, but other than the note on getting dependencies, you should not be using this.

One of the first tools that you should get if you’re hacking with GStreamer or want to play with the latest version without doing evil things to your system is probably the gst-uninstalled script. It’s the equivalent of Python’s virtualenv for hacking on GStreamer. :)

The documentation around getting this set up is a bit frugal, though, so here’s my attempt to clarify things. I was going to put this on our wiki, but that’s a bit search-engine unfriendly, so probably easiest to just keep it here. The setup I outline below can probably be automated further, and comments/suggestions are welcome.

  • First, get build dependencies for GStreamer core and plugins on your distribution. Commands to do this on some popular distributions follow. This will install a lot of packages, but should mean that you won’t have to play find-the-plugin-dependency for your local build.
  • Fedora: $ sudo yum-builddep gstreamer1-*
  • Debian/Ubuntu: $ sudo apt-get build-dep gstreamer1.0-plugins-{base,good,bad,ugly}
  • Gentoo: having the GStreamer core and plugin packages should suffice

  • Others: drop me a note with the command for your favourite distro, and I’ll add it here

  • Next, check out the code (by default, it will turn up in ~/gst/master)

  • $ curl https://cgit.freedesktop.org/gstreamer/gstreamer/plain/scripts/create-uninstalled-setup.sh | sh

  • Ignore the pointers to documentation that you see — they’re currently defunct

  • Now put the gst-uninstalled script somewhere you can get to it easily:

  • $ ln -sf ~/gst/master/gstreamer/scripts/gst-uninstalled ~/bin/gst-master

  • (the -master suffix for the script is important to how the script works)

  • Enter the uninstalled environment:

  • $ ~/bin/gst-master

  • (this puts you in the directory with all the checkouts, and sets up a bunch of environment variables to use your uninstalled setup – check with echo $GST_PLUGIN_PATH)

  • Time to build

  • $ ./gstreamer/scripts/git-update.sh

  • Take it out for a spin

  • $ gst-inspect-1.0 filesrc
  • $ gst-launch-1.0 playbin uri=file:///path/to/some/file

  • $ gst-discoverer-1.0 /path/to/some/file

  • That’s it! Some tips:

  • Remember that you need to run ~/bin/gst-master to enter the environment for each new shell
  • If you start up a GStreamer app from your system in this environment, it will use your uninstalled libraries and plugins
  • You can and should periodically update you tree by rerunning the git-update.sh script
  • To run gdb on gst-launch, you need to do something like:
  • $ libtool --mode=execute gdb --args gstreamer/tools/gst-launch-1.0 videotestsrc ! videoconvert ! xvimagesink
  • I find it useful to run cscope on the top-level tree, and use that for quick code browsing

Update: Fixed create-uninstalled.sh link to use https (thanks to Victor for pointing this out).

Introducing peerflixsrc

Some of you might have been following all the brouhaha over Popcorn Time. I won’t get into the arguments that can be made for and against at the moment.

While poking around at what it was that Popcorn Time was doing, I stumbled upon peerflix, a Node.js-based application that takes a .torrent file that points to one big video file, and presents that as an HTTP stream. It has its own BitTorrent implementation where it prioritises early chunks of the file so that it is possible to start watching the video before the entire file has been downloaded. It also seeds the file while the video is being watched locally.

Seeing as I was at the GStreamer Hackfest in Munich when this came up in discussions, it seemed topical to have a GStreamer element to wrap this neat bit of functionality. Thus was peerflixsrc born. This is a simple source element that takes a URI to a torrent file (something like torrent+http://archive.org/some/video.torrent), fires up peerflix in the background, and provides the data from the corresponding HTTP stream. Conveniently enough, this can be launched using playbin or Totem (hinting at the possibilities of what can come next!). Here’s what it looks like…

Screenshot of Totem playing a torrent file directly using peerflixsrc

Screenshot of Totem playing a torrent file directly using peerflixsrc

The code is available now. To use it, build this copy of gst-plugins-bad using your favourite way, make sure you have peerflix installed (sudo npm install -g peerflix), and you’re good to go.

This is not quite mature enough to go into upstream GStreamer. The ugliest part is firing up a Node.js server to make this work, not the least because managing child processes on Linux is not the prettiest code you can write. Maybe someone wants to look at rewriting the torrent bits from peerflix in C? There don’t seem to be any decent C-based libraries for this out there, though.

In the mean time, enjoy this, and comments / patches welcome!

GStreamer Hackfest 2014

Last weekend, I was at the GStreamer Hackfest in Munich. As usual, it was a blast — we got much done, and it was a pleasure to meet the fine folks who bring you your favourite multimedia framework again. Thanks to the conference for providing funding to make this possible!

My plan was to work on making Totem’s support for passthrough audio work flawlessly (think allowing your A/V receiver to decode AC3/DTS if it allows it, with more complex things coming the future as we support it). We’ve had the pieces in place in GStreamer for a while now, and not having that just work with Totem has been a bit of a bummer for me.

The immediate blocker so far has been that Totem needs to add a filter (scaletempo) before the audio sink, which forces negotiation to always pick a software decoder. We solved this by adding the ability for applications to specify audio/video filters for playbin to plug in if it can. There’s a now-closed bug about it, for the curious. Hopefully, I’ll get the rest of the work to make Totem use this done soon, so things just work.

Now the reason that didn’t happen at the hackfest is that I got a bit … distracted … at the hackfest by another problem. More details in an upcoming post!

Four years

Four years and what seems like a lifetime ago, I jumped aboard the ship Collabora Multimedia, and set sail for adventure and lands unknown. We sailed through strange new seas, to exotic lands, defeated many monsters, and, I feel, had some positive impact on the world around us. Last Friday, on my request, I got dropped back at the shore.

I’ve had an insanely fun time at Collabora, working with absurdly talented and dedicated people. Nevertheless, I’ve come to the point where I feel like I need something of a break. I’m not sure what’s next, other than a month or two of rest and relaxation — reading, cycling, travel, and catching up with some of the things I’ve been promising to do if only I had more time. Yes, that includes PulseAudio and GStreamer hacking as well. :-)

And there’ll be more updates and blog posts too!