[wdmaudiodev] Strange Delay with MIDI Filter Creation Times (AVStream)

  • From: Basileios Bu <basileiosbu@xxxxxxxxx>
  • To: wdmaudiodev@xxxxxxxxxxxxx
  • Date: Fri, 8 Jun 2012 17:07:26 -0400


We have a high speed USB audio device which exposes audio in(4)/out(4) and
MIDI in(1)/out(1), and we use AVStream as a driver model, which creates 4
KS filters, 2 audio, and 2 MIDI.  I am experiencing a strange issue with
the creation time of one of our MIDI filters when Skype is running in the
background (even when its told not to target our device), only on Windows
XP.  When Skype is not executing, there is no delay; I create my filter
factories without incident, and very soon after PostStart, our filters are
created by the system.  However, when Skype is executing in the background
(even when told never to address our devices), there is a delay (5-7
seconds!) between creation of the audio/MIDI input filters and  the
remaining MIDI output filter.  Even if I don't create the audio filter
factories, the aforementioned delay remains with respect to the last MIDI
filter.  I see this delay in the timestamps of WPP traces in my filter
creation calls (the last such filter created is long delayed when Skype is
in the background).  I see quite clearly in KS Studio that under the
category "KSCATEGORY_AUDIO_DEVICE" that one instance out of four lags in
creation time (which I assume to be the MIDI output instance in the general
case in which I create all 4 filters).

Note that for all cases when I create my 4 filter factories the DDI
KsCreateFilterFactory returns success, as does
KsFilterFactorySetDeviceClassesState.  I tried moving filter factory
creation and enabling to AVStrMiniDevicePostStart
from AVStrMiniDeviceStart because the docs say that
IoRegisterDeviceInterface (which is done prior to the creation of the
filter factories) must be done in the context of a system thread, which
AVStrMiniDevicePostStart seems to guarantee, but that had no effect.  The
filters are created in the context of work items, which are a limited
resource, and I tried increasing the number of work items via the registry,
but this had no effect.

Now there were some topology differences between the MS MIDI filters and
our MIDI filters, but even when I applied most of the differences, there
was no effect.  For example, I used the category "KSCATEGORY_AUDIO" instead
sum nodes, but there was no effect whatsoever, so it does not seem (to me,
at least) to be a topology issue.  On significant difference which I could
not test is that MS uses just one filter with multiple pin factories, while
the we have multiple filters with two pins factories each.  This is not a
trivial change to implement at this point, and note that the input and
output audio filter creation times are *not* similarly delayed, at least as
far as I can tell from WPP trace timestamps.

Would anyone have any idea as to the cause?  Is there any way to speed up
filter creation?  Am I possibly missing some INF registry entries?  Without
Skype, there are no large delays whatsoever. Very Strange.

Thank you for any help or insight.

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