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Grabbing audio with no audio device installed ?? RRS feed

  • Question

  • Dear all,

    am I really confused about my problem, thanks in advance to anybody knowing a solution.

    I have a source filter with two output pins (video and audio) and I am using the sample grabber filter to get the samples out of both pins. In my filter graph I connect the source filter to the sample grabber filter and to a null renderer. Everything works perfectly, until, yes until there is no audio output device on the maschine, huh. In this case only the video pin is rendered and I cant get any audio samples from the source filter (audio pin is not rendered), WHY?

    1. Does it mean that with no audio device installed (not present or disabled) it is not possible to render an audio pin with a null renderer? Note that I do not need any audio output in my case, I use a *null renderer*. Why should be any audio device needed for this, I just want to collect the samples, not to play audio.

    2. If this behaviour is by design (grrrrr), is there a workaround so that the audio pin can be connected to (through sample grabber) a null renderer filter on a computer with no audio device?

    Thanks very much

    Alex

    Friday, August 6, 2010 6:22 AM

Answers

All replies

  • 1. Does it mean that with no audio device installed (not present or disabled) it is not possible to render an audio pin with a null renderer? Note that I do not need any audio output in my case, I use a *null renderer*. Why should be any audio device needed for this, I just want to collect the samples, not to play audio.

    2. If this behaviour is by design (grrrrr), is there a workaround so that the audio pin can be connected to (through sample grabber) a null renderer filter on a computer with no audio device?


    No, this should work, irrelevant of the audio device.

    I do it all the time on servers, with no audio device. I would rather guess that you are missing some other audio graph components, such as the appropriate parser or decoder. Are you able to build the correct graph with graphedit?


    Michel Roujansky, http://www.roujansky.com

    Friday, August 6, 2010 7:14 AM
    Moderator
  • Some ACM decoders don't work when there is no audio device present.  Most non-ACM decoders work just fine.  If you suspect that as a potential cause you could install a virtual audio device (VAD), there is a sample in the DDK.
    www.chrisnet.net
    Friday, August 6, 2010 1:50 PM
  • Thanks to all.

    I realized that the source filter is causing my problem because it does not create an audio output pin if there is no audio device, which is stupid. The source filter is not under my code control. So I already contacted the filter manufacturer. But maybe something like a virtual audio device could also solve this problem, I will give it a try.

    Alex

    Friday, August 6, 2010 2:54 PM
  • Here's a 32-bit VAD build that I made a few years back to run on servers etc. that have no audio devices.  I haven't tested on Win 7 but I think it should work.

    http://chrisnet.net/msdn/Virtual_Audio_Device.zip
    www.chrisnet.net
    • Marked as answer by Alex7805 Saturday, August 7, 2010 12:49 PM
    Friday, August 6, 2010 5:07 PM
  • Thanks once again for you help.

    Alex

    Saturday, August 7, 2010 12:49 PM