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List:       linux-video
Subject:    Re: [video4linux] multiple opens/VfW
From:       alexb () jetsuite ! com (Alex Bakaev)
Date:       1998-07-29 17:48:04
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Bill Dirks wrote:
> 
> Alex Bakaev wrote:
> > my driver didn't permit multiple opens on the same channel.
> 
> Wimp! :-P
> 
Maybe. Or maybe I never envisioned more than one app using the same
capture device at once. It's more trouble than it's worth. I'd like to
see your drivers doing 2 streaming captures at once off of the same HW.

> > So I was talking about different channels when I said multiple opens.
> > What does it mean to open VIDEOIN twice?
> 
> You have two capture contexts. Two virtual devices. You can call
> DVM_FORMAT on each one and they're independent.

 The open handle is
> really a pointer to a structure that contains all the state for that
> context. 

Do you really think in my case it was different ?

When you call DVM_FRAME the corresponding virtual device gets
> real-ized onto the hardware and the frame is captured.
> 
What kind of performance were you getting ? 

> > I don't even think VfW allows for that.
> 
> By virtue of having a separate handle for each open, it does. Codecs get
> opened multiple times too. Didn't you support multiple opens on your
> codecs? You really *have* to.
> 

I didn't have codecs.

> > It's if you have multiple devices, then in makes sense.
> 
> It's as if you have as many devices as you want, but really only one.
> It's called multitasking.
> 

I appreciate the explanation. Don't think it's really useful to have
more than one app talking to the same capture HW at once though.

Alex
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