[Bug 28723] Sound stutter in Rage when emulated windows version is set to "Windows 7" (XAudio2 -> mmdevapi sound output path)

[wine-bugs at winehq.org]

http://bugs.winehq.org/show_bug.cgi?id=28723

--- Comment #75 from Alexey Loukianov <mooroon2 at mail.ru> 2011-12-08 11:16:14 CST ---
(In reply to comment #74)
> >pump-out 2*alsa_period audio data in advance
> How? Rage only gives you 10ms and you cannot predict the future.

Well, we can "predict" with a pretty high probability that if an app acquire
some pointers to WASAPI COM interfaces, calls IAC_Initialize() followed by
IAC_Start() - it's going to playback some sound :-). Making small alsa_period a
hard requirement would left behind an unfortunate user whose hardware is not
capable of using small periods. IMO it'd be better to still have sound produced
but lagging way behind (due to 2*alsa_period lead-in silence chunk) than not to
have sound at all. Yes, we would need to pump-out 2*alsa_period lead-in silence
again in case of xrun but as we're talking about case when ALSA isn't capable
of using small periods - chances to hit xrun are pretty slim. And yes, if the
minimal period that device supports is - say - 1s, then it would end up in
sound lagging 2s at the worst case (and slightly more than 1s at best). It's
bad, but it's still better than having no sound at all. Of course we should
warn user loudly in such case. 

> I've read that PulseAudio uses snd_pcm_rewind to overwrite (when mixing)
> already written data with new samples.  You could try out that route however my
> experience with seeking with snd_pcm_forward is bad, see bug #28517.

No-no-no-no-no, it is "not a way to go". I've seen vast amount of different
failures caused by bugs in various parts of ALSA (kernel drivers, alsalib,
plugins and so on) which arise when you try to use rewind/forward. Using these
would introduce more problems (esp. on older systems like CentOS 4 or 5) than
it's expected to solve.

PS. BTW, in bug #28517 you had mentioned the following test case:
"...I've been thinking about an audible test with two streams with 180° phase
delta not written at the same time, yet they should all enter the same 10ms
period and might annihilate themselves...". I'm thinking about trying to
implement it this weekend. It'd be pretty curious to take a look at the results
:-).

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