[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 #115 from Jörg Höhle <hoehle at users.sourceforge.net> 2011-12-23 04:49:04 CST ---
It's too early to close this underrun bug.  The current design doesn't prevent
it.  Consider these scenarios:
a) 10ms prefill -- This is the Rage use-case.
   write 10ms iff padding <= 10ms (=period)

b) without prefill.
It's the same really. ALSA simply starts 10ms later as data comes in.

c) App takes a little time, calling ReleaseBuffer only 6ms after the event.
That doesn't matter, the app has time to supply data until the next callback
event.

d) The callback is delayed a little due to system load.
This is the killer.

Consider a 10ms ALSA period. At each and every event, ALSA is on the verge of
underrun, having consumed the meagre 10ms it was given. If the callback is
late, an underrun is due.

Consider a 16ms ALSA period. ALSA won't start at the first event, because the
period is not full.  This actually does good as it is equivalent to a lead-in. 
However, at time t=26ms, ALSA has finished playing its 16ms period, whereas
mmdevapi has only seen 30ms.  32ms is needed for the next period, hence an
underrun is due.  Or is likely, depending on the inner ALSA device workings,
e.g. hw:0 may start to play the incomplete period and see it filled up at time
t=30ms.  Whereas we've seen in comment #63 that plug:dmix won't play the
incomplete period, yet maybe its internal buffering will allow it to absorb the
delay until t=30.

Here's a timeline:
0    10   20   30   40   50   60   70   80   90  100  110  120
|....|....|....|....|....|....|....|....|....|....|....|....|... 10ms
     |.......|.......|.......|.......|.......|.......|.......|.. 16ms
----- prefill
   20-----        20ms are available at time t=10ms
        30-----   30ms at t=20ms
             40-----   40ms at t=30ms
                  50-----

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