[wdmaudiodev] Re: How to adjust lip-sync for WaveCyclic driver using GetPosition()
- From: "Bielik, Robert" <Robert.Bielik@xxxxxxxxx>
- To: "wdmaudiodev@xxxxxxxxxxxxx" <wdmaudiodev@xxxxxxxxxxxxx>
- Date: Sat, 8 Jun 2013 06:11:19 +0000
Hi Philip,
To my knowledge there is no mechanism today in Windows to accommodate for
latencies in the HW chain. In WaveRT there is a possibility to query the driver
for HW latencies, but normally they're so small so it does not matter much for
lip-sync accuracy anyway.
That's why (almost?) all video players have the possibility to offset the video
wrt audio position.
Regards,
/Rob
-----Original Message-----
From: wdmaudiodev-bounce@xxxxxxxxxxxxx
[mailto:wdmaudiodev-bounce@xxxxxxxxxxxxx] On Behalf Of Philip Gruebele
Sent: den 8 juni 2013 00:53
To: wdmaudiodev@xxxxxxxxxxxxx
Subject: [wdmaudiodev] How to adjust lip-sync for WaveCyclic driver using
GetPosition()
Hi All.
I have a WaveCyclic (msvad based) USB audio driver. It works perfectly except
for one issue: lip-sync is not perfect and I would like to compensate for
hardware/USB latencies to fix this.
According to MS docs, GetPosition() should start incrementing when in the RUN
state. Also, GetPosition() is supposed to return the current sample position
which is being output by the speakers. For my driver, there is about 30ms of
USB buffering and then the USB audio device also buffers about 30ms. This
amounts to a total hardware latency of 60ms.
Since GetPosition() is supposed to return the buffer position currently being
output by the DAC, this means that after entering KS_RUN state,
GetPosition() should return 0 for about 60ms, and only then start to increment
(since the hardware is not outputting the sample data for the first 60 ms).
The problem is that when GetPosition() is implemented to stay at position 0 for
60ms, WaveCyclic stops calling CopyTo() and the render stream stalls.
Does anyone know why this happens? Is this a bug in Wavecyclic? It should not
stall under these conditions, right? This is how hardware latency should be
handled no? The buffer size I report back to WaveCyclic is large enough to
handle 60ms of data, and CopyTo() stalls after just 30ms... It's a mystery.
One can repeat this problem by simply modifying MSVAD to return 0 for 60ms
after entering KS_RUN state.
Any help is much appreciated!
Thanks
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