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Present Perfect

Work weekend

Filed under: couchdb,DAD,GStreamer,Hacking,Music — Thomas @ 10:18 am

10:18 am

Since we are doing our yearly business planning weekend later this week, I had reserved the weekend to do work – mainly, put together eight (strike that, nine, our CEO added one at the 11th hour Sunday evening) presentations. But I wasn’t getting into the groove of things, and procrastination hit.

So I wondered, what’s the single most important thing that’s been on my mind and that I’d do right now if I didn’t have anybody else to answer to ?

And the answer was simple – I started another rewrite of DAD (Digital Audio Database) last year, this time based on CouchDB. I was in the middle of splitting up into a core (defining all base classes and simple implementations without any dependencies; for example, a pickle-based storage of the mixing data), a dadgst module (for a GStreamer-based player, since I will also have a pure web-based player), and a dadcouch module (for a CouchDB storage backend).

Before the split-up it was mostly a hardcoded GStreamer player playing from the pickle file, and a bunch of scripts to analyze files and put them into the pickle. I had not properly finished the CouchDB conversion – mostly, a bunch of methods that previously were synchronous now had to be made asynchronous with deferreds, and that was causing some conceptual issues (like, how to a lot of deferreds together – when chaining doesn’t work, and parallellizing brings down your computer).

So, that’s what I wanted to do this weekend first – get the couchdb backend to a state where it can select tracks slicing the audiofiles and providing the mixing information, and use the data from the old DAD database of now seven years ago. I want to hear those old songs again, according to my preference, and properly mixed. And with that in place, after a few hours of hacking, I could focus myself completely on the presentation preparing.

Well, completely except for the baby visits, the family lunching, and the pregnant friend visiting.

If you like looking at not-completely-finished-code that probably only I can get running usefully anyway, start here.

LongoMatch 0.16.0 packaged

Filed under: Fedora,GStreamer — Thomas @ 7:26 pm

7:26 pm

After recording a video at work this week, I needed a way to go through it and identify interesting points. So Andoni suggested I gave LongoMatch a try and package it for Fedora.

LongoMatch is a digital coach, useful to tag and analyze sport matches. We didn’t actually play sports, but it was still useful for my purpose. I now have thirty short clips that someone else can now edit into a useful video.

Packages are available for Fedora 13 and 14 in my repo.

First GStreamer conference

Filed under: Conference,GStreamer — Thomas @ 4:55 pm

4:55 pm

I’m in Cambridge (the UK one, not the US one) for the first ever GStreamer conference!

Years ago when I was in a cabin in the middle of the woods in Norway at four kilometers away from the closest main road and cut off by waistdeep snow, I never imagined that today I would be attending a conference dedicated to GStreamer with 150 people. 150 !

It seems the conference is a good mix between professionals and hobbyists. I’ve seen a few interesting applications built on top of GStreamer. Pretty cool stuff.

I took a quick look at the conference schedule and out of 19 talks, seven of them are from people that have been employed by the Fluendo group in the past, and for most of them it was their first full-time GStreamer job. It’s great to see these people branched out to other companies and taking GStreamer with them and higher up!

All in all, looks like the GStreamer community is in good shape. Next year, we’ll need two days…

While we’re at it, we should be handing out ’10 years of GStreamer badges’ to the people that have stuck by us so long :)

Train shedding

Filed under: Conference,Flumotion,GStreamer,Hacking — Thomas @ 3:57 am

3:57 am

Had a good time at the OpenVideo Conference in New York City, as well as today at (cut short for me) FOMS.

I took the Amtrak train from NYC to Boston and was looking forward to doing four hours of hacking, knocking up a quick prototype of doing chunked streaming of Ogg and WebM.

I didn’t actually get to that point however because my test stream triggered the streamer going lost, meaning that its main loop is stuck. So attaching gdb I was reminded how the ‘pystack’ macro in gdb (which was incredibly useful – it prints a python stack) hasn’t worked for me for the last couple of years.

And this time I set out to properly fix it. If only the docs on gdb were easy to understand. My knowledge of gdb doesn’t go much beyond the standard ‘thread apply all bt’ stuff and doing simple inspection. I ended up understanding why the macro hangs (it compares the value of $pc to known function names, and goes up the stack until it finds PyMain. In most of my cases there is no PyMain however, and when you go ‘up-silent’ in gdb at the top of the stack, it just silently fails leaving you at the same frame forever).

I don’t claim to understand exactly how gdb works; for example, there are cases where $pc stays the same going up a frame, seemingly because a function is wrapped into a macro which seems to get its own frame. So I ended up writing a loop that goes up until the $pc changes, and then go back down, leaving me at the frame that calls a python method with a code object.

So, now I have my pystack working again in the cases I tested, so that’s good.

Incidentally, if anyone knows gdb well enough, here are some questions:

  • Is there a way I can detect in a script that ‘up’ didn’t actually go up ?
  • Is there a programmatic way to know how many frames there are, and what frame number you’re on ?

After fixing that, I was again bitten by a bug where – not always, but often – a flow with Vorbis and Theora has a timestamp/duraiton discontinuity of 1 nanosecond. I can’t reproduce it on the command line with -launch, so I think it’s related to a set_base_time call on the pipeline.

So I started writing a unit test, but for some reason make check in gst-plugins-base doesn’t work for me because it can’t find capsfilter and other core elements. So I get to dive into the test setup code again to figure out why a registry is getting generated that blacklists coreelements…

The train pulled into Boston as I was looking into how the new registry code works and why it blacklists coreelements, so I’ll have to save this test for a later day…

Incidentally, I have a day off in Boston this week. I really want to finally go to MIT and follow a class there, in computer science or mathematics. Is that sort of thing open in the US ? Can you just sit in on a class ? Any tips ?

We’ve come a long way, baby

Filed under: GStreamer — Thomas @ 1:20 pm

1:20 pm

Linux Magazine March 2010 is full of GStreamer goodness: one article reviewing 4 media players, all of them using GStreamer (Banshee, Rhythmbox, Amarok 2, Songbird), and a three page article on your favourite video editor, PiTiVi!

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