It’s that time of the year again…

Which time of the year? The time when Google announces the new Summer of Code!

Okay so you know I”m not always very positive about the outcome of Summer of Code work, even though I’m extremely grateful to Constanze (and Mike, who got it i tree now!) for the work on filesystem based capabilities — I’m pretty sure at this point that it also has been instrumental for the Hardened team to have their xattr-based PaX marking (I’m tempted to re-consider Hardened for my laptops now that Skype is no longer a no-go, by the way). Other projects (many of which centred around continuous integration, with no results) ended up in much worse shape.

But since being always overly negative is not a good way to proceed in life, I’m going to propose a few possible things that could be useful to have, both for Gentoo Linux and libav/VLC (whichever is going to be part of GSoC this year). Hopefully if something comes out of them is going to be good.

First of all, a re-iteration of something I’ve been asking of Gentoo for a while: a real alternatives-like system. Debian has a very well implemented tool for selecting among alternative packages supporting multiple tools. In Gentoo we have eselect — and a bunch of modules. My laptop counts 10 different eselect packages installed, and for most of them, the overhead of having another package installed is bigger than the eselect module itself! This also does not really work that well, as for instance you cannot choose the tar command, and pkg-config vs pkgconf require you to make a single selection by installing one or the other (or disabling the flag from pkgconf, but that defeats the point, doesn’t it?).

Speaking of eselect and similar tools, we still have gcc-config and binutils-config as their own tools, without using the framework that we use for about everything else. Okay, the last guy who tried to make these bit more than he could chew, and the result has been abysmal, but the reason there is likely that the target was set too high: re-do the whole compiler handling so that it could support non-GCC compilers.. this might actually be too small a project for GSoC, but might work as a qualification task, similar to the ones we’ve got for libav in the past.

Going to libav, one thing that I was discussing with Luca, J-B and other VLC developers, was the possibility to integrate at least part of the DVD handling that is currently split between libdvdread and libdvdnav into libav itself. VLC already forked the two libraries (and I rewrote the build system) — me and Luca were looking into merging them back into a single libdvd library already… but a rewrite and especially one that can reuse code from libav, or introduce new code that can be shared, would probably be a good thing. I haven’t looked into it but I wouldn’t be surprised if libdvbpsi could follow the same treatment.

Finally, another project that could sound cool for libav would be to create a library, API and ABI compatible with xine, that only uses libav. I’m pretty sure that if most of the internals of xine are dropped (including the configuration file and the plugin system), it would be possible to have a shallow wrapper around libav instead of having a full blown project. It might lose support for some files, such as modules, and DVDs, but it would probably be a nice proof of concept and would show what we still need .. and the moment when we can deal with those formats straight into libav, we know we have something better than simply libav.

On a similar note, one of the last things I’ve worked on, in xine, was the “audio out conversion branch”, see for instance this very old post — it is no more no less than what we now is libavresample, just done much worse. Indeed, libavresample actually has the SIMD-optimized routines I never found out how to actually write, which makes it much nicer. Since xine, at the moment I left it, was actually quite nicely using libavutil already, it might be interesting to see what happens if all the audio conversion code is killed, and replaced with libavresample.

So these are my suggestions for this season of GSoC, at least for the projects I’m involved on… maybe I’ll even have time to mentor them this year, as with a bit of luck I’ll have stable employment when the time comes for this to happen (more on this to follow, but not yet).

One thought on “It’s that time of the year again…

  1. The alternatives system exists and is in the science overlay. It has been working there for a while and we have already started discussing moving it to the main tree. One issue was that it was heavily borrowed from Exherbo, but from what I saw so far the original authors seem to be OK with it. We will probably need to do that sooner rather than later as some libraries are in urgent need of being updated.Denis.


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