[pulseaudio-tickets] [Bug 87202] Strong noise (unintelligible) when playing through the analog output using mmap

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=87202

--- Comment #7 from Mario Sanchez Prada <msanchez at gnome.org> ---
After so much testing and gdb debugging today I finally identified the problem
in alsa-lib, after following the lead from the experiment mentioned in "Note
1", and it seems to be caused by the call to snd_pcm_mmap_begin() returning the
wrong memory chunks in the areas array, leading to the strange noise mentioned.

With that in mind, I started looking inside of alsa-lib, and found significant
differences between the latest code in the 0.28 release and the one I've
available in my environment, which is quite older (0.25). And even better, I
found that just upgrading to that newer version of alsa-lib would get rid of
the noise, so indeed it seems the problem was there!

I've devoted a bit more of time to try to find the specific changeset and it
seems that the the fix for bug 64299 is the one fixing this specific:

http://git.alsa-project.org/?p=alsa-lib.git;a=commitdiff;h=f2d39afe6139ab16aa2aeea0f51f32db79ab1262

I found that commit by simply looking at the changelog and looking for things
related to either mmap or rewinds, and then applying it locally to my package
as a patch on top, so I'm pretty certain that it fixes the problem. Still, I
would appreciate if someone (maybe David, as the author) could comment on
whether this makes sense, so we can maybe resolve this bug as a duplicate or
invalid.

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