[wdmaudiodev] Re: PC Audio Capture

  • From: NCH Obble Smith <Obble@xxxxxxxxxxxxxxx>
  • To: wdmaudiodev@xxxxxxxxxxxxx
  • Date: Fri, 08 Jan 2010 13:20:54 +1100

Yes, I check every 5ms, and I use 2 buffers, 1st is the dma buffer and 2nd is a copy of the previous audio data so when I compare the 2, I know how much new audio was overwritten the style audio. I then wait til theres 10ms of free audio and start reading, every so ofter checking I am now too close or too far. With Vista it's buffer was 69ms long, but Win7 was 20ms ( 2x 10ms) that was very hard to get right until I learnt to increase the mutlimedia timer to support 5ms reading/ checking times.

I am aware that setting at the end of every poll the thread the media timer to 5ms will be a little more of a drain on battery life, but it had to be done to prevent the out of sync / overlapping new & old in a 10ms read cycle.

Also as a side note, I once asked where to get the audio format, and I was told it one of the properties being past. I found it is actually in IRP_Create request in stack->FileObject->FileName.Buffer. Using the format:
#pragma pack (1)
struct CreatePinRequest {
   WCHAR szPath[39]; //{[KSNAME_PIN]}\
   KSPIN_CONNECT pinConnect;
   union {
      KSDATAFORMAT ksData;
   } Format;

Thats correct for XP/Vista/Win7. (Of course it's technically possible for it not to be a DSOUND/WAVEFORMATEX format, but thoses unique / rare formats I can't handle in my app anyway.)


On 8/01/2010 1:05 PM, Tim Roberts wrote:
NCH Obble Smith wrote:
May I ask why that can't be done?  As I have done it in my audio
filter that runs in XP/Vista/Win7.   With Vista/Win7,  it reads from
that DMA buffer.
So, you're chasing the buffer circular pointers?  That's dangerous,
isn't it?  You don't net notifications when the pointers move.  Are you


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