I've been looking at this some more. It seems that what you
suggested, using two audio sgchannels within the same grabber, won't
work around my problem since I still need to be able to start and
stop different grabs independently. As far as I can tell, SGStop on
any sequence grabber is stopping all SGAudioChannels regardless of
which sequence grabber they're associated with. That seems to be a
bug, would you agree?
As far as I can tell the only workarounds seem to be: 1) do different
captures from different processes or 2) capture by accessing the vdig
directly rather than through the sequence grabber.
Does that seem right?
On Dec 13, 2005, at 12:01 AM, Brad Ford wrote:
On Dec 12, 2005, at 11:25 PM, Erin Tomson wrote:
Hi. I'm trying to write an application based on the WhackedTV
sequence grabber code that captures audio and video from multiple
sources to separate files at once.
I'm able to configure two sequence grabbers components, each with
both an audio and a video channel. I start the first recording to
one file, then the second recording to another file. However, when
I stop the first sequence grabber, the audio stops at that point
in the second capture as well. The video in the second continues
being recorded until I stop the second sequence grabber.
Are the two grabs grabbing from different audio devices, or the
same device? What about audio preview device? Are they using the
same audio preview device?
This is using the an SGAudioChannel, but I tried using a
SoundMediaType SGChannel as well without luck.
SoundMediaType SGChannel definitely will not work. SGAudioChannel
can capture from multiple devices within the same grab. That is a
well tested code path. You cannot capture from the same device in
two different grabs because of the problem of device control. Any
sgchannel can call SGStop or SGStartRecord, which will stop/start
up the audio device.
If all else fails, create two audio sgchannels within the same
grabber. If you want to grab the audio to different files, you can
use the SGDataProc to write the files yourself.
I can't see anything except the call to SGStop() on the first
grabber that would cause the second grabber to stop recording
audio. Does anyone have any suggestions as to what I should look
into? Are there any known issues with recording multiple files
from multiple sources at once?
The issues you are seeing are all centered around the fact that you
are trying to share a resource between multiple grabs, all of which
can record/preview/stop independently of one another. If you
restrict yourself to a single grab, all these problems will go away.
-Brad Ford
QuickTime Engineering
I'm using an AlchemyTV card and a Pyro A/V Link DV Converter, if
hardware makes any difference.
Thanks ahead of time for any suggestions or pointers!
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