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Thread: xf86-video-v4l Driver Ported To V4L2

  1. #1
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    Default xf86-video-v4l Driver Ported To V4L2

    Phoronix: xf86-video-v4l Driver Ported To V4L2

    One of the seldom mentioned X.Org DDX drivers is xf86-video-v4l. This driver is not for some obscure or vintage hardware like many other drivers in the X.Org tree (e.g. -savage, -s3virge, -tseng, -trident) but it targets no specific graphics card and instead provides an X-Video extension port for video overlay. Just load the module and it works with any hardware supported by a Video 4 Linux (V4L) driver. While this driver isn't often worked on (the most recent commits in Git are from July), it's in the process of being revised...

    http://www.phoronix.com/vr.php?view=OTA4Nw

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    Okay, I know what V4L is and I've read this article, the README and the man page, but I still don't understand what this driver actually does. Help?

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    Quote Originally Posted by Chewi View Post
    Okay, I know what V4L is and I've read this article, the README and the man page, but I still don't understand what this driver actually does. Help?
    Thanks for beating me to the punch, I was about to ask the same. For me, V4L (1/2) has to do with support for (web)cameras. Does this module have anything to do with that?

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    V4L is not just for cameras. It's what allows you to see TV when you have a TV card (analog, digital or satelite). Those cards have a framebuffer. So I guess xf86-video-v4l allows you to run X11 on your TV card?

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    My first guess was that it rendered X into a V4L-compatible device node so that you could capture it with mencoder or the like. But it talks about real V4L hardware so that's not it.

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    Quote Originally Posted by RealNC View Post
    V4L is not just for cameras. It's what allows you to see TV when you have a TV card (analog, digital or satelite). Those cards have a framebuffer. So I guess xf86-video-v4l allows you to run X11 on your TV card?
    That doesn't make any sense. A TV tuner is an input device, not an output device.

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    Mauro Carvalho Chehab himself has written:

    http://permalink.gmane.org/gmane.com...rg.devel/18623

    What the driver basically does is to check the Xv extension of the screen, using
    xf86XVQueryOffscreenImages(), selecting a FOURCC mode that it is compatible with
    a video capture board. Then, it passes a memory address at the video board where
    the overlay should be placed to the kernel driver. The kernel driver will then
    program the device's DMA to do data transfer from the capture board into the
    video board.

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    Okay........... nope.

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    Some video devices do have video out

    I'm guessing this driver allows you to show you session rather than just output something you're playing

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    I only took a guess at what it does. Reading the description, I can only see how it does whatever it is it does, with no explanation at all about what it actually does.

    So, what does it do?

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