But passing the file name as argument to a py.test invocation selects only the doctest from that file (wtf!?). Instead, you need to call it like this:

This is documented in the section advanced test selection and running modes of the py.test documentation, although I fail to see how this is advanced.

There were a number of interesting Talks. I especially liked the talk of our DPL, and those about piuparts and git-buildpackage. In contrast to the other LinuxTag talks, we had a livestream of our talks and recorded (most) of them. The kudos for setting this up goes to Alexander Wirt, who spent quite a few hours to get it up and running.

I have to apologize for being late in bringing my Notebook, which was intended to do the theora encoding of the livestream. This was a misunderstanding on my part, I should have known that this is not going to be setup in the night before show time… So to compensate the extra hours he had to put in for me, I offered to do the post processing of the videos.

Basic approach for post processing

The main goal of post processing the videos was (of course) to compress them to a usable size from the original 143 GB. I also wanted to have a title on each video, and show the sponsors at the end of the video.

My basic idea to implement that consisted of the following steps:

1. Create a title animation template.
2. Generate title animations from template for all talks.
3. Use a video editor to create a playlist of the parts title – talk – epilogue.
4. Run the video editor in batch mode to generate the combined video.
5. Encode the resulting video as ogg theora.

As always with technology, it turned out that the original plan needed a few modifications.

Title animations

Originally I wanted to use Blender for the title animation, but I knew it is quite a complicated bit of software. So I looked for something simpler, and stumbled across an article that pointed me towards Synfig Studio for 2D animation. This is also in Debian, so I gave it a try.

I was delighted that Synfig Studio has a command line renderer which is just called synfig and that the file format is XML, which would make it simple to batch-create the title animations. My title template can be found in this git repository.

Batch creation of title animations

I used a combination of make and a simple python script to replace the author name and the title of the talk into the synfig XML file. The data for all talks is another XML file talks.xml. Basically, I used a simple XPath expression to find the relevant text node and change the data using the ElementTree API of lxml python module.

The same could be done using XSLT of course (for a constant replacement, see this file) but I found it easier to combine two XML files in python.

Note that I create PNG files with synfig and use ffmpeg to generate a DV file from those. Originally, I had synfig create DV files directly but those turned out quite gray for some reason. I am now unable to reproduce this problem.

Combining the title animation with the talk

For joining the title animation with the talk, I originally went with OpenShot, which somebody of the video team had running at the conference. My idea was to mix a single video manually and just replace the underlying data files for each talk. I expected that this would be easy using the openshot-render command, which renders the output video from the input clips and the OpenShot project file. However, OpenShot stores the video lengths in the project file and will take those literally, so this did not work for talks of different play times…

I considered working with Kino or Kdenlive but they did not look more appropriate for this use case. I noticed that OpenShot and Kdenlive both use the Media Lovin’ Toolkit under the hood, and OpenShot actually serializes the MLT configuration to $HOME/.openshot/sequence.xml when rendering. I first tried to read that XML file from python (using the mlt python bindings from the python-mlt2 package) but did not find an API function to do that. So I just hard coded the video sequence in python.

I ran into a few gotchas on the way:

• it’s easy to segfault MLT from Python (something is wrong with the refcounting)
• generating ogg theora using MLT from Python (which uses libavformat) resulted in a bad audio/video synchronisation of the output (more than 1 second for 1 hour of video)
• generating dv from MLT and running ffmpeg2theora on the result is disk-bound on my quad core system – so use a pipe to ffmpeg2theora

Things to improve

While the results look quite okay for me now, there is a lot of room for improvement.

• What bothers me the most is the unequal audio volume between talks. We should apply something like replay gain for normalization. I did not find an easy way to add this to the processing pipeline, otherwise it would have been included already.
• Original recordings have different aspect ratios, so after combining them, there is a letterbox added. This is the case for Goswin’s talk on Multiarch for example. I’d rather have the title distorted or letter boxed, if I get around to it, I will fix it in the script.
• Most of the recordings concentrate on showing the slides. As we did not keep the raw camera data, but recorded the DVswitch output, we missed the opportunity to show the speaker more often in full screen. Looking at the same slide becomes quite boring after half a minute, so it would be better
  to show the speaker more often. That would require quite a bit of man power for post processing though, I have to admit that I did not watch all the hours of video.
• We could cut a bit off the talk at start and end, when the speaker discusses where he is available for questions. It is not of interest anymore after the conference is over.

Availability

• git repo (browsing): http://www.landschoff.net/git/?p=mdc-video.git;a=summary
• git repo (clone): git://landschoff.net/mdc-video
• Videos: http://meetings-archive.debian.net/pub/debian-meetings/2010/minidebconf-berlin/ (note: most of these are in german, apart from the DPL and the LXDE talk)

All required packages are installed by the following command:

apt-get install lighttpd trac subversion apache2-utils

We install lighttpd together with trac, as otherwise the trac package will pull in an installation of apache2, which is a bit more heavyweight than what I wanted.

Setting up the directory tree

Let’s set up a directory tree for trac:

for p in env svn auth; do mkdir -p /srv/trac/$p/demo; done

One directory for the trac environment data, another for the subversion repository and the third for authentication data. Putting all environments into a single directory (/srv/trac/env) would allow to run a single trac server for all environments using the TRAC_ENV_PARENT_DIR configuration variable.

Creating a trac environment

The trac environment is created using

trac-admin /srv/trac/env/demo initenv

The command will ask interactively for the following settings:

• Project name: Enter a name as you like (“Demo”). Note that you can change this later.
• Database connection string: You can accept the default sqlite database.
• Repository type: I used the default “svn” selection.
• Path to repository: /srv/trac/svn/demo

From now on, we can access the (empty) trac instance by running tracd --port 8000 /srv/trac/env/demo and accessing the trac-integrated web server at port 8000 of the server. Hit Ctrl-C to kill the tracd after you don’t need it any longer.

Creating an initial user

By default, trac creates no users. Only anonymous access is allowed, which by default is read-only. Therefore, we have to create a user to add content. Let’s use digest authentication:

htdigest -c /srv/trac/auth/demo/users "trac demo realm" admin
trac-admin /srv/trac/env/demo permission add admin TRAC_ADMIN

You can now start tracd with authentication:

tracd --port 8000 \
    --auth=demo,/srv/trac/auth/demo/users,"trac demo realm" \
    /srv/trac/env/demo

Configure lighttpd

To use lighttpd to serve the trac environment, we first need to fix the permissions:

chown -R www-data /srv/trac/env
chmod +x /usr/share/pyshared/trac/web/fcgi_frontend.py

I think, the second command should not be required and filed Debian bug #510441 because of this.

Next, we need a configuration file. It delegates the trac path to a FastCGI handler and contains the location of the authentication data. Copy the configuration file to /etc/lighttpd/conf-available/ and enable the configuration:

lighty-enable-mod auth trac-demo
/etc/init.d/lighttpd force-reload

The trac instance should be available at http://HOSTNAME/trac. Have fun!

Automatic setup

For my own tests I wrote a script which does most of this automatically. Use at your own risk!

BTW: All of this was tested against Debian lenny (not released at time of writing).