Olivier's adventures in Wonderland - Geekeries

Where is my bike?

Olivier Tilloy — Wed, 11 Aug 2010 19:58:00 +0200

Almost two years ago I wrote a little Python script that retrieves availability information for the bicing network in Barcelona. My grand plans to use that script to optimize my morning routine didn’t quite see the light, but the script itself seems to have proved useful to others.

Earlier this year, Eskerda contacted me to let me know that he was interested in writing an application for android to assist bicing users in cycling the city efficiently. As bicing.cat’s servers are dead slow, hitting them directly from each running instance of the application was not an option, so he came up with the idea of a static resource hosted on Google App Engine and updated regularly, using my script.

The result is OpenBicing, a cool application for android. I don’t own an android phone myself, so I couldn’t test it, but it looks really fancy, I particularly like the radius mode. Bonus point, it’s Free Software (Apache license).

And as if it wasn’t good enough, Eskerda set to work to support more bike sharing networks with the same model. OpenSevici and OpenVélib are two standalone applications that respectively cover the networks of Sevilla and Paris.

In an effort to gather them all in a single application in an extensible way, CityBikes was born. Android users and cyclers, go check it out, and don’t forget to send your feedback to the author!

Note to self: consider buying a new phone…

pyexiv2 0.2.2 released

Olivier Tilloy — Thu, 27 May 2010 12:29:00 +0200

I'm happy to announce that pyexiv2 0.2.2, codename "Holiday", was released today.

This is a maintenance release that fixes two memory leaks, optimizes the use of the underlying libexiv2 (expect performance improvements), improves the API documentation, restores access to the image comments (was a regression from the 0.1 series) and adds an optional parameter to preserve timestamps when writing metadata.

The source tarball and a Windows installer (compiled and tested against Python 2.6.5) are already available, and packages for Ubuntu 10.04 will follow shortly in pyexiv2 developers' PPA.

As usual, feedback, suggestions and bug reports are welcome!

pyexiv2 - the best choice for photo metadata manipulation in python

Olivier Tilloy — Wed, 07 Apr 2010 11:38:00 +0200

Franz is presenting pyexiv2 in glowing terms on his blog in an article titled « pyexiv2 - the best choice for photo metadata manipulation in python ».

His opinion, as a real user and photographer, counts a lot. And the article is a very good (much better than what I could have come up with) introduction to what pyexiv2 is and can be used for.

This will no doubt bring in interest and new users and contributors aboard, and will ultimately benefit to everyone. Thanks Franz!

pyexiv2 0.2 is out

Olivier Tilloy — Thu, 25 Mar 2010 18:31:00 +0000

After almost two years of pretty irregular development, I am happy to announce that pyexiv2 0.2.0, codename "Commuting", was released today.

It is essentially a re-write of the 0.1 branch, with a new, more flexible API (and is therefore not backward compatible with the previous releases).

It is compiled against libexiv2 0.19, and among others things, it features:

Support for reading and writing XMP metadata;
Support for reading images from stream;
A fully documented API (including a tutorial and detailed instructions for developers);
Compiled and tested on Linux and Windows (bonus: a Windows installer is available!);
A battery of unit tests that reasonably cover the code base.

Many thanks to everyone who contributed time, bug reports, patches and suggestions!

As usual, feedback is welcome!

pyexiv2 0.2 pre-release testing

Olivier Tilloy — Mon, 25 Jan 2010 23:20:00 +0000

As I mentioned on the pyexiv2-developers' mailing list, I believe the 0.2 branch of pyexiv2 is now ready for pre-release testing.

Progress on this pet project of mine has been very slow due to the lack of spare time I had to dedicate to it, and constant context-switching. But it finally reached a state where I think it is complete and stable enough to form the basis of a first release.

There are still some missing bits (complete documentation and a windows installer are the two big items on my list), but the functionality is there and I'd love to see it stress-tested and get as much feedback as possible. The bazaar branch can be grabbed from lp:pyexiv2, it should be compiled against the latest release of libexiv2, 0.19. Bug reports and questions are welcome!

Going to FOSDEM

Olivier Tilloy — Thu, 14 Jan 2010 00:09:00 +0000

I will be in Brussels from the 5th to the 7th of February for the tenth edition of FOSDEM. Kaleo, Guijemont, Ugo and Fernando are also going, it should be a fun week-end.

I'm looking forward to attending interesting talks and above all meeting the Free Software crowd IRL.

Oh, and of course, I can't wait for the Friday Beer Event! If you plan to be there, drop me a line to schedule a round or two of Belgian beer.

Bicing Barcelona

Olivier Tilloy — Sun, 19 Oct 2008 17:06:30 +0000

One of the things that make life easy in Barcelona is its efficient public transportation system. Living in the suburb, every morning I take the train to go to work. When I arrive at Plaza Catalunya, I am almost there but there is still a good 20 minutes walk to go to the World Trade Center. That would be without Bicing, the community bicycle program that allows me to get a bike with my RFID card, cycle down the Ramblas and drop it at one of the stations next to the entrance of the WTC. Well, in theory...

Like many good ideas, Bicing is a victim of its own success. In the morning, a hell of a lot of people use Bicing to commute to work, and as there is quite a lot of people who work in the WTC, the two stations, with merely 60 spaces, are very early full of bikes. The solution comes in the form of vans that patrol the city, collect bikes from the full stations and repopulate the empty ones, to equilibrate the flow. Unfortunately the action of these vans is not fast enough in rush hours, and in the morning it is not uncommon to have to wait for quite some time before the van, awaited as the messiah by a dozen of commuters, shows up.

So I came up with the idea of collecting data about the stations I am interested in as a user. This data would, hopefully, help me predict in a reliable manner when and where I am sure to find some space to park a bike, so as to adapt and optimize my morning routine (that is, which train I should take). Bicing provides on their website a map of the city with the stations and the availability of the bikes in real-time. They are using Google Maps' API to build this map, and although the result is quite fancy, everybody seems to agree it is not really usable because too small (and really slow). There are some alternatives provided by users, more usable but still not quite what I am looking for. Until Bicing decides to provide an open API, let's scrape some data!

To the point directly, the two questions to answer are:

Where to get the data from?
How to get it?

Once this is answered, it is just a matter of writing a quick script that will do the job. Now, here are the answers:

http://bicing.com/localizaciones/localizaciones.php
A regular expression: exml.parseString$'(.*)'$;, and an XML parser

In fact when one browses the map and clicks one station to get the information about the availability of the bikes, the data is not updated real-time. One has to reload the page for fresh data. And all the data is stored as XML in a piece of Javascript, in a call to this exml.parseString method.

I wrote a quick Python script that retrieves the data, parses the XML and populates a list of stations with the available information (name, GPS coordinates, bikes available and free spaces). It is licensed under the GPLv3, well documented and available as a bzr branch on Launchpad at: lp:~osomon/+junk/bicing (you can also browse and download the code at http://bazaar.launchpad.net/~osomon/+junk/bicing/files).

Now I need to find how to make the most of this data. I was thinking of regularly polling for a given set of stations over a given period of time, storing the data and then drawing a graph, to better understand the data. I will probably publish my findings in a next article, stay tuned!

Playing with GStreamer

Olivier Tilloy — Thu, 03 Jan 2008 22:45:33 +0000

I recently got to appreciate the possibilities offered by GStreamer when I started playing with my new toy and the videos it records.

Nothing to say about the videos themselves, except that the quality is really good, with a maximum resolution of 640x480, sound (mono), and a maximum length of 10 minutes, more than enough for short video clips. Not that I shoot lots of video clips, but I do from time to time and for the sake of archiving them I needed to fix the rotated videos (a really bad habbit of mine to shoot with my camera rotated 90° clockwise), and of course store them in an open format that I'm sure can be decoded even in 50 years.

For this purpose, GStreamer seemed like the perfect tool. By default the videos, once transferred to my laptop, open with Totem (with GStreamer as a backend). There was the first glitch: no sound for my videos in Totem, and as a side effect, the video would sometimes not play (but sliding a little bit would trigger it correctly). However, both VLC and MPlayer could successfully decode both the video and the sound. A quick look at the console output of MPlayer showed that indeed the sound is not decoded by FFmpeg, which kind of explains why GStreamer cannot decode it:

ISO: File Type Major Brand: Original QuickTime
Quicktime/MOV file format detected.
VIDEO:  [avc1]  640x480  24bpp  29.970 fps    0.0 kbps ( 0.0 kbyte/s)
xscreensaver_disable: Could not find XScreenSaver window.
GNOME screensaver disabled
==========================================================================
Opening video decoder: [ffmpeg] FFmpeg's libavcodec codec family
Selected video codec: [ffh264] vfm: ffmpeg (FFmpeg H.264)
==========================================================================
==========================================================================
Forced audio codec: mad
Opening audio decoder: [imaadpcm] IMA ADPCM audio decoder
AUDIO: 44100 Hz, 1 ch, s16le, 177.1 kbit/25.10% (ratio: 22136->88200)
Selected audio codec: [imaadpcm] afm: imaadpcm (IMA ADPCM)
==========================================================================

Whatever the imaadpcm audio codec is, I could not find any GStreamer plugin (good, ugly or bad) to decode it. So the solution I came up with was to use MPlayer to extract the audio track to PCM uncompressed sound and then use the GStreamer magic to encode it in the suitable format (namely Vorbis) and remux it with my video into an Ogg container, previously encoded to a suitable format itself (namely Theora).

Here is how to extract the audio track using MPlayer (will be dumped to a file named audiodump.wav):

mplayer -vc null -vo null -ao pcm -benchmark video.mov

Here is how to play the extracted sound using gst-launch:

gst-launch filesrc location=audiodump.wav ! wavparse ! osssink

I won't go into details on how to use gst-launch to build and test GStreamer pipelines, the man page is a good pointer to start, and there exist a bunch of good tutorials. Here is a slightly more complicated pipeline that encodes the extracted audio track to Ogg Vorbis:

gst-launch filesrc location=audiodump.wav ! wavparse ! audioconvert ! vorbisenc ! oggmux ! filesink location=audio.oga

Next step is to extract and decode the video:

gst-launch filesrc location=video.mov ! qtdemux ! ffdec_h264 ! xvimagesink

We can now play both the video and audio parts in sync:

gst-launch filesrc location=audiodump.wav ! wavparse ! osssink filesrc location=video.mov ! qtdemux ! ffdec_h264 ! xvimagesink

Almost there, now let's encode everything and stuff it into an ogg container:

gst-launch filesrc location=audiodump.wav ! wavparse ! audioconvert ! vorbisenc ! oggmux name=muxer muxer. ! filesink location=video.ogv filesrc location=video.mov ! qtdemux ! ffdec_h264 ! theoraenc ! muxer.

Now rotating the video is just a matter of adding a videoflip element to the pipeline (can you guess where?), and the quality of the resulting video can be adjusted with the properties of the vorbisenc and theoraenc elements.

With the help of a simple shell script gathering these elements and placed in my $HOME/.gnome2/nautilus-scripts/, I can rotate and re-encode my videos with a simple click in Nautilus. Easy!

Now the next step would be to add relevant metadata to the videos, such as the author, the place where it was shot and the date and time. Unfortunately, according to Wikipedia, "Currently, there is no official standard for including metadata in Ogg containers [...] Metadata must currently be included in the codec. There is fairly good software support for Vorbis metadata — often referred to as comments. But software support for Theora and FLAC comments in Ogg containers is very limited." Yes, it sucks... The solution is to go with the Vorbis comments, but it does not seem feasible to set tags using only gst-launch (or did I miss something?): one needs to develop a GStreamer application, using for example one of the numerous bindings. Needless to say, I'm going for the Python one!

FOSDEM 2007

Olivier Tilloy — Mon, 26 Feb 2007 21:40:00 +0000

I haven't been blogging for some time now (almost 5 months, wow) but I cannot resist making a report of what has been a fantastic week-end. I was in Brussels, Belgium, for three days, mostly attending the FOSDEM conferences and enjoying the rich and subtile flavours of belgian beers.

This was my first time in a free software summit, and I must say I am not disappointed! There was a huge number of beards per square meter and one could feel geekiness in the air. All these developers, ranging from the free software guru to the anonymous hacker (and I am one of them), these thrilling conferences, the no less thrilling conversations with other hackers, great ideas emerging from technical discussions, all of this was just great.

The week-end really started on Friday night, when I arrived at the youth hostel in the city centre where I met Guijemont. From there we headed towards the Roy d'Espagne, a famous pub on the Grand' Place, where the pre-FOSDEM Friday beer event is held before every edition, in a huge room full of hackers from all over Europe (and even further). Waitresses carrying big trays full of belgian beers were trying to keep up with our drinking pace, it must have been a trying night for them!

The serious stuff started on Saturday morning, in Université Libre de Bruxelles, with the first conference, Software patents in Europe by Pieter Hintjens. Then Jim Gettys gave an impressive presentation of the OLPC project, which is amazing. Knowing that making free software allows us, in a way, to make the world better is a great feeling.

After a lunch break, a round of all the stands (Mozilla, Debian, Gentoo, FSFE, Ubuntu, Google, FreeBSD, and many others) and bringing my modest donation to FOSDEM (I got a nice t-shirt!), back to the lecture and developers rooms with lots of interesting stuff: X.Org by Keith Packard (or how to explain the correlation between hacking on X and heavy drinking), What's new in GStreamer by Edward Hervey (whom I had met at a party in Barcelona), Linux Kernel by Andrew Morton, Django by Pim Van Heuven (or how to make web development sexy), and finally Gnome apps with Scheme by Andy Wingo (also seen in Barcelona). In the afternoon, Kaleo joined us, freshly arrived from Barcelona, and Toto also came from Lille. That was the Hull Dream Team reloaded!

It had been a rich day, and the best way to conclude it was in a pub around a few pints, after a well deserved dinner in a restaurant.

After a short night, the show went on with, again, lots of conferences. In the morning, I attended Security testing by Pete Herzog, Metasploit Framework by its main developer, H. D. Moore (very impressive features for security probing), and Elisa by Philippe Normand (Kaleo's project leader, also met in Barcelona). After a short lunch break, Kaleo has to leave to catch his flight back to Spain.

We then attended OpenOffice.org - OpenXML by Michael Meeks and the end of Miguel de Icaza's presentation of Mono, during which an asshole made pointless remarks in a terribly bad english, confusing Linux, open source, proprietary software, profit making... The living proof that, yes, in the free software world too, we have our lot of jerks (although this one was an award winning one, and I tend to think the proportion of such persons in such an event is very low, he was probably the only one). We stayed in the same lecture room for the presentation of GDB tracepoints and their use in kernel debugging, by Jim Blandy, and then Federico Mena Quintero's Profiling Desktop Applications. This guy is a real showman and he knows his topic, now I really want to hack on Gnome (if only days were more than only 24 hours...) !

If you ever doubted it, here is the truth: APIs are like big green monster hidden in flower pots.

We finished with a presentation entitled Linux in embedded security devices by Jan Veldeman, a bit disappointing on the contents, but no regret as there were no other conferences at that time.

And that was it, in a flashlight FOSDEM 2007 was already over, my head was full of great stuff, ideas, projects, a little bit disorientated by the lack of sleep, we headed towards the bus stop under the rain.

Bye bye Brussels, see you next year! And thank you so much to the volunteers who organised all this so well and made it possible, you guys did a wonderful job!

tilloy.net

Olivier Tilloy — Thu, 28 Sep 2006 17:40:19 +0000

Ayant terminé mes études à l'IIE, je n'aurai donc bientôt plus accès aux services d'ARISE.

Plus de shell sur perso, plus d'hébergement web et de bases de données, il me fallait donc migrer ce blog vers les serveurs d'un autre hébergeur. J'ai donc choisi un hébergement mutualisé chez Lost Oasis. Jusqu'ici, service de bonne qualité, à un prix raisonnable, et bonne réactivité des administrateurs. J'en ai profité pour acheter un nom de domaine, me voilà donc propriétaire de tilloy.net.

J'ai profité de la migration pour mettre à jour ma version de DotClear (passage de la 1.2.1 à la 1.2.5, comme sur des roulettes, et j'attends la version 2 avec impatience), renommer quelque peu les catégories et réordonner certains billets pas à leur place.

Mettez à jour vos liens et marque-pages!

http://tilloy.net/olivier
http://tilloy.net/olivier/blog