Tag: f/oss

August 17, 2010

Updates from the Rygel + DLNA world

Things have been awfully quiet since Zeeshan’s posted about the work we’ve been doing on DLNA support in Rygel. Since I’ve released GUPnP DLNA 0.3.0, I thought this is a good time to explain what we’ve been up to. This is also a sort of expansion of my Lightning Talk from GUADEC, since 5 minutes weren’t enough to establish all the background I would have liked to.

For those that don’t know, the DLNA is a consortium that aims to standardise how various media devices around your house communicate with each other (that is, your home theater, TV, laptop, phone, tablet, …). One piece of this problem is having a standard way of identifying the type of a file, and communicating this between devices. For example, say your laptop (MediaServer in DLNA parlance) is sharing the movies you’ve got with your TV (MediaPlayer), and your TV can play only upto 720p H.264-encoded video. When the MediaServer is sharing files, it needs to provide sufficient information about the file so that the MediaPlayer knows whether it can play it or not, so that it can be intelligent about what files show up in its UI.

How the DLNA specification achieves this is by using “profiles”. For each media format supported by the DLNA specification, a number of profiles are defined, that identify the audio/video codec used, the container, and (in a sense) the complexity of decoding the file. (for multimedia geeks, that translates to things like the codec profile, resolution, framerate/samplerate, bitrate, etc.)

For example, if a file is indicated to be of a DLNA profile named AAC_ISO_320, this indicates that this is an audio file encoded with the AAC codec, contained in an MP4 container (that’s “ISO”), with a bitrate of at most 320 kbps. Similarly, a file with profile AVC_MP4_MP_SD_MPEG1_L3 represents a file with H.264 (a.k.a. AVC) video coded in the H.264 Main Profile at specific resolutions upto 720×576, MP3 audio, in an MP4 container (there are more restrictions, but I don’t want to swamp you with details).

So now we have a problem statement – given a media file, we need to get the corresponding DLNA profile. It’s easiest to break this problem into 3 pieces:

Discovery: First we need to get all the metadata that the DLNA specification requires us to check. Using GStreamer and Edward’s gst-convenience library, getting the metadata we needed was reasonably simple. Where the metadata wasn’t available (mostly codec profiles and bitrate), I’ve tried to expose the required data from the corresponding GStreamer plugin.
DLNA Profiles: I won’t rant much about the DLNA specification, because that’s a whole series of blog posts in itself, but the spec is sometimes overly restrictive and doesn’t support a number of popular formats (Matroska, AVI, DivX, OGG, Theora). With this in mind, we decided that it would be nice to have a generic way to store the constraints specified by the DLNA specification and use them in our library. We chose to store the profile constraints in XML files. This allows non-programmers to tweak the profile data when their devices resort to non-standard methods to work around the limitations of the DLNA spec.
Matching: With 1. and 2. above in place, we just need some glue code to take the metadata from discovery and match it with the profiles loaded from disk. For the GStreamer hackers in the audience, the profile storage format we chose looks suspiciously like serialized GstCaps, so matching allows us to reuse some GStreamer code. Another advantage of this will be revealed soon.

So there you have it folks, this covers the essence of what GUPnP DLNA does. So what’s next?

Frankie Says Relax: Since the DLNA spec can often be too strict about what media is supported, we’ve decided to introduce a soon-to-come “relaxed mode” which should make a lot more of your media match some profile.
I Can Haz Trancoding: While considering how to store the DLNA profiles loaded from the XML on disk, we chose to use GstEncodingProfiles from the gst-convenience library since the restrictions defined by the DLNA spec closely resemble the kind of restrictions you’d expect to set while encoding a file (codec, bitrate, resolution, etc. again). One nice fallout of this is that (in theory), it should be easy to reuse these to transcode media that doesn’t match any profile (the encodebin plugin from gst-convenience makes this a piece of cake). That is, if GStreamer can play your media, Rygel will be able to stream it.

Apart from this, we’ll be adding support for more profiles, extending the API as more uses arise, adding more automated tests, and on and on. If you’re interested in the code, check out (sic) the repository on Gitorious.

August 17, 2010

GUADEC 2010 :(

Hopefully that title was provocative enough. ;) No, GUADEC seemed to be a smashing success. If only I had been able to attend instead of lying in bed for 2 days, ill and wondering at the general malignancy of a Universe that would do this to me.

Collabora Multimedians, looking for a canal

Nevertheless, I had a great time meeting all the cool folks at Collabora Multimedia at our company meeting. Managed to trundle out for my Rygel + DLNA lightning talk (more updates on this in a subsequent post). Things did get better subsequently, and I had an amazing week-long vacation in Germany, and now I’m back at home with my ninja skillz fully recharged!

April 5, 2010

Site moved to Linode

I finally got tired of how slow NearlyFreeSpeech.net is (it’s still a fantastically affordable service – you get what you pay for and more), and moved to a Linode. Setup and migration was dead simple, and I’m really happy with the instance I’m on (and extremely happy about their awesome service). Do feel free to drop me a note if anything on the site doesn’t work for you.

p.s.: This also adds to my count of Gentoo boxen. :)

February 21, 2010

Pure EFI Linux Boot on Macbooks

My company was really kind to get me a Macbook Pro (the 13.3-inch “5.5” variant). It is an awesome piece of hardware! (especially after my own PoS HP laptop I’ve been cussing at for a while now)

That said, I still don’t like the idea of running a proprietary operating system on it (as beautiful as OS X is ;)), so I continue to happily use Gentoo. The standard amd64 install works just fine with some minor hiccups (keyboard doesn’t work on the LiveCD, kernel only shows a console with vesafb).

The one thing that did bother me is BIOS-emulation. For those coming from the PC world, Macs don’t have a BIOS. They run something called EFI which is significantly more advanced (though I think the jury’s out on quirkiness issues and Linus certainly doesn’t approve of the added complexity).

Anyway, in order to support booting other OSes (=> Windows) exactly as they would on PCs, Apple has added a BIOS emulation layer. This is how Ubuntu (at least as of 9.10) boots on Macbooks. Given that both the bootloader (be it Grub2 or elilo) and the Linux kernel support booting in an EFI environment, it rubbed me the wrong way to take the easy way out and just boot them in BIOS mode. There is a reasonable technical argument for this – I see no good reason to add one more layer of software (read bugs) when there is no need at all. After a lot of pain, I did manage do make Linux boot in EFI-only mode. There is not enough (accurate, easily-findable) documentation out there, so this is hard-won knowledge. :) I’m putting this up to help others avoid this pain.

Here’s what I did (I might be missing some stuff since this was done almost a month ago). The basic boot steps look something like this:

EFI firmware starts on boot
Starts rEFIt, a program that extends the default bootloader to provide a nice bootloader menu, shell, etc.
Scans FAT/HFS partitions (no ext* support, despite some claims on the Internet) for bootable partitions (i.e. having a /efi/… directory with valid boot images)
Runs the Grub2 EFI image from a FAT partition
Loads the Linux kernel (and initrd/initramfs if any) from /boot
Kernel boots normally with whatever your root partition is

Now you could use elilo instead of Grub2, but I found this it to not work well (or at all) for me, so I just used a Grub2 (1.97.1, with some minor modifications) (just adds an “efi” USE-flag to build with --with-platform=efi). While I could make /boot a FAT partition, this would break the installkernel script (it’s run by make install in your kernel source directory), which makes symlinks for your latest/previous kernel image.

Instructions for installing the Grub2 EFI image are here. Just ignore the “bless” instructions (that’s for OS X), and put the EFI image and other stuff in something like /efi/grub (the /efi is mandatory). You can create a basic config file using grub-mkconfig and then tweak it to taste. The Correct Way™ to do this, though, is to edit the files in /etc/grub.d/.

Of course, you need to enable EFI support in the kernel, but that’s it. With this, you’re all set for the (slightly obsessive-compulsive) satisfaction of not having to enable yet another layer to support yet another proprietary interface, neither of which you have visibility or control over.

February 11, 2010

FOSSKriti ’10 \o/

Three days left to the event I helped start 3 years ago. That’s right, folks, FOSSKriti ’10 is here!

We started this event in 2008 because there was a huge gap between the open source world and academia in India. The aim was to expose enthusiastic students to what the F/OSS world has to offer, how they can participate in the community, contribute, and get that warm, happy feeling in the gut. :) And I’ve met enough people who make me believe that we have been successful in this endeavour.

One complaint we always get is that we are not newbie-friendly. From the beginning, we took an active call to channel our limited resources towards encouraging people to just start hacking and contributing (that’s the important part, remember?), which necessarily meant that if this was your first exposure to the F/OSS world, things could be a bit overwhelming.

This time, the organising team is trying something different. FOSSKriti ’10 will have loosely have 2 tracks. One track is like previous editions of the event – it’s meant for people who are comfortable with coding, possibly already F/OSS hackers. The agenda, I am given to understand, is “Come – Sit – Fork – Code – Share LuLZ.” :) And being privy to what some of the FOSSKriti veterans are planning, I am extremely excited about what this track will bring.

The second track is meant for students who are enthusiastic about F/OSS but need a little more guidance with getting started. There will be talks and workshops to help them get bootstrapped, and hopefully provide them with sufficient resources to take the ball and run. The schedule for this track is already up.

This is not complete, so keep an eye out for updates. Unfortunately, again, I will not be able to make it to the event. :( If you’re a student in India, interested in F/OSS, possibly not too far from Kanpur, this is an event you cannot miss!

January 16, 2010

(Gst)Discovering Vala

My exploits at Collabora Multimedia currently involve a brief detour into hacking on Rygel, specifically improving the DLNA profile name guessing. We wanted to use Edward‘s work on GstDiscoverer work, and Rygel is written in Vala, so the first thing to do was write Vala bindings for GstDiscoverer. This turned out to be somewhat easier and more difficult than initially thought. :)

There’s a nice tutorial for generating Vala bindings that serves as a good starting point. The process basically involves running a tool called vapigen, which examines your headers and libraries, and generates a GIR file from them (it’s an XML file describing your GObject-based API). It then converts this GIR file into a “VAPI” file which describes the API in a format that Vala can understand. Sounds simple, doesn’t it?

Now if only it were that simple :). The introspected file is not perfect, which means you need to manually annotate some bits to make sure the generated VAPI accurately represents the C API. These annotations are specified in a metadata file. You need to include things like “the string returned by this function must be freed by the caller” (that’s a transfer_ownership), or, object type Foo is derived from object type FooDaddy (specified using the base_class directive). Not all these directives are documented, so you might need to grok around the sources (specifically, vapigen/valagidlparser.vala) and ask on IRC (#vala on irc.gnome.org).

All said and done, the process really is quite straightforward. The work is in [my gst-convenience repository][arun-gst-conv-ks.git] right now (should be merged with the main repository soon). I really must thank all the folks on #vala who helped me with all the questions and some of the bugs that I discovered. Saved me a lot of frustration!

I’ve already got Rygel using these bindings, though that’s not been integrated yet. More updates in days to come.

December 29, 2009

GNOME Day @ FOSS.IN/2009

Yes, yes, I know this post is a tad late, but hey, it’s still the right year. ;)

As Srini had announced, Dec 5th was GNOME Day at FOSS.IN this year. We kicked the day off with Shreyas giving a developer’s introduction to GNOME 3.0. This was followed by another well-received talk by Srini on the Mobiln2 UI and Clutter.

By the end of lunch, it turned out our already packed schedule had got some new additions from the other enthusiastic GNOME folks around! The afternoon session was kicked off by Arun ‘vimzard’ Chaganty introducing what newbies need to know to dive into GNOME development. Tobias Mueller followed with a talk about GNOME Bugsquadding. Sayamindu and Dimitris then took the stage for a short L10n talk. Next up was a talk about Anjal by Puthali. Olivier then gave a hackers’ introduction to Empathy/Telepathy, Srinidhi and Bharath did a quick introduction to using the OpenSUSE Build Service.

Wait, I’m not done yet. :) The final session on GNOME Performance was a 4-hit combo with me giving a quick introduction to Sysprof, Lennart introducing mutrace, Krishnan giving a pretty wow introduction to using DTrace to profile GNOME, and Dhaval giving a short introduction to how cgroups could help make GNOME more responsive.

Phew! That was a long and awesome day, with some icing on the cake in the form of stickers and T-shirts. The last were possible thanks to the GNOME Foundation, so a huge thanks to them!

The times they are a-changin’

Yesterday was my last day at NVidia. I’ve worked with the Embedded Software team there for the last 15 months, specifically on the system software for a Linux based stack that you will see some time next year. I’ve had a great time there, learning new things, and doing everything from tweaking bit-banging I²C implementations with a CRO to tracking down alleged compiler bugs (I’m looking at you -fstrict-aliasing) by wading through ARM assembly.

As some of you might already know, my next step, which has had me bouncing off the walls for the last month, is to join the great folks at Collabora Multimedia working on the PulseAudio sound server. I’ll be working from home here, in Bangalore (in your face, 1.5-hour commute!). It is incredibly exciting for me to be working with a talented bunch of folks and actively contributing to open source software as part of my work!

More updates as they happen. :)

July 12, 2009

It’s pronounced Gwahdec

I’ve been terrible about it, but here’s the big update — I just got back today after spending the last week at the Gran Canaria Desktop Summit, location of the first co-located GUADEC and aKademy. It’s been amazing, and I don’t know where to start. Let’s try the beginning.

The GNOME Foundation has funded a very significant part of my expense for this trip (making it possible at all), so a huge thanks to Travel Committee for giving me this opportunity. :) To summarise …

Of communities and respect

I feel old a lot, these days. It’s been about 17 years since I first sat in front of a computer (and, soon after, realised I’d be sitting in front of them for a very long time to come). It’s been about 11 years since I intrepidly stuck in a Red Hat Linux (before it was called PCQLinux ;-)) CD into my CD-ROM drive and started a voyage that continues to this day. And it’s been about 10 years since I saw the first flame-wars amidst the Indian F/OSS community. Not much has changed in all this time. I am still incredibly passionate about computing, I still love Linux and the F/OSS world for the freedom, and some Indian F/OSS communities still have a tendency to shoot themselves in the foot as soon as it starts to show some promise.

I don’t know what it is about us — perhaps we are inherently political animals, and have some basic need to take an opposing stand. Or maybe there are just enough of us that this automatically happens. Or maybe it’s not even inherently an Indian problem. It’s bound to happen in any group, and is not, in itself, a problem. What is a problem is respect. In any reasonably large group, there are bound to be people who don’t like each other. Sometimes they might even be able bring themselves to have a shred of respect for each other (an extreme that is unfortunately seen all-too-often). What is unforgivable, though, is failure to respect the community.

When you start arguing with someone, on IRC, a mailing-list, or even in person, always remember that by making the flames personal, you are disrespecting the community. By dragging everyone around you into the mud, you are sowing the seed of trouble and strife. You end up forcing people to take a side or walk away, effectively killing the community.

My post here comes from painfully watching this happen too many times. Even more so from watching it happen now. So here’s my request, nay plea — if you’re in the midst of such a tiff, take a moment to see what it’s doing to the community you’re in (I’m assuming we’re well past the “assume good will” stage here — you did start with “assume good will”, didn’t you?). If nothing else, find a way to keep what’s personal separate.

Addendum: If you’re one of the folks who shake their head and walk away when this happens, here’s my plea to you — don’t walk away. Point out to the people responsible that their personal quarrels are not germane to the community, and ask them to take it off the community’s channels of communication. If enough people did this, maybe some sense would prevail.

Note: I’m leaving comments open for constructive discussion.

Note2: In case I come off sounding like I am innocent of all this, these are lessons that I have learned the hard way.

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