[Bug 28039] IAudioClock_GetPosition must ignore underruns (MacOS)

[wine-bugs at winehq.org]

http://bugs.winehq.org/show_bug.cgi?id=28039

--- Comment #7 from Jörg Höhle <hoehle at users.sourceforge.net> 2011-12-17 16:16:17 CST ---
The remaining issue becomes obvious when increasing the sleep even more, e.g.
to 3150ms:
render.c:1090: data at 0x422dc000 for prefill 20671
render.c:1119: hpctime 3151 after 3150ms
render.c:1138: hpctime 3252 pcpos 3252
render.c:1143: padding 0 position 20671/20671 slept 3250ms iteration 0
# normal padding 0 past underrun
render.c:1138: hpctime 3352 pcpos 3352
render.c:1143: padding 0 position 41342/41342 slept 3350ms iteration 1
render.c:1166: Test marked todo: GetBuffer large (20671) at iteration 1

WineCoreAudio 1.3.35 pretends advancing by 20671 frames within 100ms(!), as if
underrun had never occurred during the last 3 seconds.

render.c:1138: hpctime 3453 pcpos 3453
render.c:1143: padding 0 position 62013/62013 slept 3450ms iteration 2
render.c:1166: Test marked todo: GetBuffer large (20671) at iteration 2
render.c:1138: hpctime 3553 pcpos 3553
render.c:1143: padding 0 position 82684/82684 slept 3550ms iteration 3
render.c:1166: Test marked todo: GetBuffer large (20671) at iteration 3
... advancing by 1.5 seconds worth of frames within 300ms.

This behaviour is bogus and reminds of ALSA's dmix at the time Wine used the
"play silence during underruns" mode instead of XRUN that I reported in bug
#28517, comment #4. There too, the app could throw megabytes of data to the
audio engine, normalizing only once as many frames had be written fast as the
underrun gap had caused.
A difference probably is: ALSA plays silence, CoreAudio might buffer all that
stuff and play it late. I can't tell as my render tests are solely playing
silence.

The resulting behaviour is very different from native and may cause havoc with
apps using winmm, because GetPosition governs WHDR_DONE messages. They will be
sent out too fast after an underrun occurred, causing loss of sync and other
effects.

The good news is that GetPosition will not report a position higher than the
number of written frames.

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