Arun Raghavan

Extremely pithy tagline here

TAG: gentoo

PulseAudio 4.0 and Skype

This is a public service announcement for packagers and users of Skype and PulseAudio 4.0.

In PulseAudio 4.0, we added some code to allow us to deal with automatic latency adjustment more gracefully, particularly for latency requests under ~80 ms. This exposed a bug in Skype that breaks audio in interesting ways (no sound, choppy sound, playback happens faster than it should).

We’ve spoken to the Skype developers about this problem and they have been investigating the problem. In the mean time, we suggest that users and packagers work around this problem in the mean time.

If you are packaging Skype for your distribution, you need to change the Exec line in your Skype .desktop file as follows:

Exec=env PULSE_LATENCY_MSEC=60 skype %U

If you are a user, and your distribution doesn’t already carry this fix (as of about a week ago, Ubuntu does, and as of ~1 hour from now, Gentoo will), you need to launch Skype from the command line as follows:

$ PULSE_LATENCY_MSEC=60 skype

If you’re not sure if you’re hit but this bug, you’re probably not. :-)

grsec and PulseAudio (and Gentoo)

This problem seems to bite some of our hardened users a couple of times a year, so thought I’d blog about it. If you are using grsec and PulseAudio, you must not enable CONFIG_GRKERNSEC_SYSFS_RESTRICT in your kernel, else autodetection of your cards will fail.

PulseAudio’s module-udev-detect needs to access /sys to discover what cards are available on the system, and that kernel option disallows this for anyone but root.

PulseAudio 2.0: Twice The Goodness!

That’s right, it’s finally out! Thanks go out to all our contributors for the great work (there’s too many — see the shortlog!). The highlights of the release follow. Head over to the announcement or release notes for more details.

  • Dynamic sample rate switching by Pierre-Louis Bossart: This makes PulseAudio even more power efficient.

  • Jack detection by David Henningsson: Separate volumes for your laptop speakers and headphones, and more stuff coming soon.

  • Major echo canceller improvements by me: Based on the WebRTC.org audio processing library, we now do better echo cancellation, remove the need to fiddle with the mic volume knob and have fixed AEC between laptop speakers and a USB webcam mic.

  • A virtual surround module by Niels Ole Salscheider: Try it out for some virtual surround sound shininess!

  • Support for Xen guests by Giorgos Boutsiouki: Should make audio virtualisation in guests more efficient.

We don't always make a release, but when we do, it's awesome

Special thanks from me to Collabora for giving me some time for upstream work.

Packages are available on Gentoo, Arch, and probably soon on other distributions if they’re not already there.

Gentoo: PulseAudio + ALSA update

For a long time now, fellow-Gentoo’ers have had to edit /etc/asound.conf or ~/.asoundrc to make programs that talk directly to ALSA go through PulseAudio. Most other distributions ship configuration that automatically probes to see if PulseAudio is running and use that if avaialble, else fall back to the actual hardware. We did that too, but the configuration wasn’t used, and when you did try to use it, broke in mysterious ways.

I finally got around to actually figuring out the problem and fixing it, so if you have custom configuration to do all this, you should now be able to remove it after emerge’ing media-plugins/alsa-plugins-1.0.25-r1 or later with the pulseaudio USE flag. With the next PulseAudio bump, we’ll be depending on this to make the out-of-the-box experience a lot more seamless.

This took much longer to get done than it should have, but we’ve finally caught up. :)

[Props to Mart Raudsepp (leio) for prodding me into doing this.]

PulseAudio 1.1 (the echo release?)

Yep, if we keep this up, it could even become a habit!

PulseAudio 1.1 is out. It’s mostly a bunch of bug fixes on top of 1.0. Most important of these are fixes for: a libpulse dependency on libsamplerate (if enabled) which would make our LGPL license invalid, broken Skype audio capture (because we changed from a 3 number version to 2 numbers), broken startup without a DBus session bus running, and not going crazy on USB disconnects.

This should be a very safe upgrade, so grab it while it’s hot!

Alternate sample rates

I’ve just pushed a bunch of patches by Pierre-Louis Bossart that can have a pretty decent CPU/power impact. These introduce the concept of an “alternate sample rate”.

Currently, PulseAudio runs all your devices at a default sample rate, which is set to 44.1 kHz on most systems (this can be configured). All streams running at different sample rates are resampled to this sample rate. Pierre’s patches add an alternate sample rate that we try to switch to under certain circumstances if it means that we can save on resampling cost. This would happen if the stream uses exactly the alternate sample rate, or some integral-or-so multiple of it.

The default value for the alternate sample rate is 48 kHz. So if you’re playing a movie off a DVD where the audio track is typically a 48 kHz stream, and your card supports it, we switch to 48 kHz and avoid resampling altogether. Similarly, while making voice calls, common sample rates are 8, 16, and 32 kHz. These can be resampled to 48 kHz much faster than to 44.1 kHz.

Now for the big caveat — this won’t work if there’s any other stream connected to your sink/source. So if your music player is playing (or even paused) when you get that voip call, we can’t update the rate. This situation can probably be improved by at least allowing corked streams have their sample rate change (so having some random stream connected but not playing — I’m looking at you, Flash! — won’t block rate updates altogether). Hopefully we’ll get this fixed before this feature is released in PulseAudio 2.0.

Thanks to Pierre for all his work on this, and to my company, Collabora, for giving me some time for upstream work!

1.w00t!

As Colin Guthrie reports, PulseAudio 1.0 is now out the door! There’s a lot of new things in the release, and we should be getting a much more regular release schedule going. Head over to the full release notes for more details.

A lot of people have contributed to this release and thanks to them all. Special props to Colin all the patch-herding, tireless help, and code ninjutsu!

p.s.: Gentoo packages are already available, of course. :)