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List:       mjpeg-users
Subject:    Re: [Mjpeg-users] ZR36057: Capturing compressed and uncompressed
From:       "Ronald S. Bultje" <rbultje () ronald ! bitfreak ! net>
Date:       2007-05-01 19:02:38
Message-ID: 4FA66E15-AD59-4383-9BC7-1E8342223DE5 () ronald ! bitfreak ! net
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Hi Markus,

On April 25, Markus Schwab wrote:
> We use the Zoran Corporation ZR36057PQC Video cutting chipset to  
> capture
> simultaneously compressed and uncompressed videos (after patching the
> kernel, to allow multiple opens on video devices). This works fine in
> the 2.4'er kernel series.

Using the same applicaton or different applications? If same, using  
the same or different file descriptors?

> So my question is, if there is a solution for both capturing  
> compressed
> and uncompressed videos simultaneously?

Not really supported, although it should work, _if_ from different  
fds or different apps. From the same fd/app, it cannot work, b/c you  
share the same memory segment in the mmap() call. This cannot  
possibly work. Essentially, you're capturing JPEG and raw frames in  
the same buffer. this is awfully wrong. I think there's protections  
in the kernel to make sure this never happens. It shouldn't hang,  
though, it should error out...

> Is it supported at all or just good luck that it works with kernel  
> 2.4?

Pure luck, in 2.4 at least. The fact that kernel patching was  
required should say enough. 2.6 protects from this happening.

Ronald




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