Getting DTS 5.1+ sound via S/PDIF or HDMI using PulseAudio

While PCs still usually provide a full set of analog jacks capable of outputting a 5.1 audio, other modern hardware (such as TVs) is usually limited to digital audio outputs (and sometimes analog outputs limited to stereo sound). These outputs are either S/PDIF (coaxial or optical) or HDMI. When the PC is connected to a TV, a pretty logical setup is to carry the sound via HDMI to the TV, and from there via S/PDIF or HDMI ARC to a 5.1 amplifier. However, it isn’t always as simple as it sounds.

For a start, S/PDIF is a pretty antiquated interface originally designed to carry stereo PCM audio. The modern versions of the interface have sufficient bandwidth for up to 192 kHz sampling rate and up to 24 bit audio depth. However, in order to support more than two audio channels, the transmitted sound needs to be compressed. S/PDIF hardware usually supports MPEG, AC3 and DTS formats.

HDMI is better there. HDMI 1.2 technically supports up to 8 channels of PCM audio, 2.0 up to 32 channels. However, not all hardware actually supports that. In particular, my TV seems to only support stereo PCM input, and ignores additional channels when passed 5.1 audio. Fortunately, additional audio channels work when compressed input is used. HDMI supports more audio formats, including DTS-HD MA and TrueHD.

In this post, I’d like to shortly explore our options for making a PulseAudio-enabled Linux system output compressed 5.1 over S/PDIF or HDMI (apparently both are treated the same from ALSA/PulseAudio perspective).
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The ultimate guide to EAPI 8

Three years ago, I had the pleasure of announcing EAPI 7 as a major step forward in our ebuild language. It introduced preliminary support for cross-compilation, it finally provided good replacements for the last Portagisms in ebuilds and it included many small changes that made ebuilds simpler.

Only a year and a half later, I have started working on the initial EAPI 8 feature set. Similarly to EAPI 6, EAPI 8 was supposed to focus on small changes and improvements. The two killer features listed below were already proposed at the time. I have prepared a few patches to the specification, as well as the initial implementation of the respective features for Portage. Unfortunately, the work stalled at the time.

Finally, as a result of surplus of free time last month, I was able to resume the work. Along with Ulrich Müller, we have quickly prepared the EAPI 8 feature set, got it pre-approved, prepared the specification and implemented all the features in Portage and pkgcore. Last Sunday, the Council has approved EAPI 8 and it’s now ready for ~arch use.

What’s there in EAPI 8? Well, for a start we have install-time dependencies (IDEPEND) that fill a gap in our cross-compilation design. Then, selective fetch/mirror restriction make it easier to combine proprietary and free distfiles in a single package. PROPERTIES and RESTRICT are now accumulated across eclasses reducing confusion for eclass writers. There’s dosym -r to create relative symlinks conveniently from dynamic paths. Plus bunch of other improvements, updates and cleanups.

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Retiring the multilib project

I created the Multilib project back in November 2013 (though the effort itself started roughly a year earlier) with the goal of maintaining the multilib eclasses and porting Gentoo packages to them. Back in the day, we were even requested to co-maintain a few packages whose maintainers were opposed to multilib ports. In June 2015, last of the emul-linux-x86 packages were removed and our work has concluded.

The project continued to exist for the purpose of maintaining the eclasses and providing advice. Today, I can say that the project has served its purpose and it is time to retire it. Most of the team members have already left, the multilib knowledge that we advised on before is now common developer knowledge. I am planning to take care of the project-maintained eclasses personally, and move the relevant documentation to the general wiki space.

At the same time, I would like to take this opportunity to tell the history of our little multilib project.

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From build-dir to venv — testing Python packages in Gentoo

A lot of Python packages assume that their tests will be run after installing the package. This is quite a reasonable assumption if you take that the tests are primarily run in dedicated testing environments such as CI deployments or test runners such as tox. However, this does not necessarily fit the Gentoo packaging model where packages are installed system-wide, and the tests are run between compile and install phases.

In great many cases, things work out of the box (because the modules are found relatively to the current directory), or require only minimal PYTHONPATH adjustments. In others, we found it necessary to put a varying amount of effort to create a local installation of the package that is suitable for testing.

In this post, I would like to shortly explore the various solutions to the problem we’ve used over the years, from simple uses of build directory to the newest ideas based on virtual environments.
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