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xf86-video-v4l Driver Ported To V4L2

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  • 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

  • #2
    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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    • #3
      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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      • #4
        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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        • #5
          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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          • #6
            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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            • #7
              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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              • #8
                Okay........... nope.

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                • #9
                  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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                  • #10
                    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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                    • #11
                      The driver exposes v4l devices as Xv ports. It is not a conventional ddx and doesn't allow you to run X on your v4l device. It's basically a helper module so that the v4l devices can stream data directly to an Xv buffer in GPU accessible memory, saving some memcpys when displaying video from the v4l device.

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                      • #12
                        Aaaaah. Thanks, Alex.

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                        • #13
                          I have a TV card. I just enabled the v4l module in my xorg.conf. When starting X, I only get a blank screen and the system freezes. Need to reboot though SysRq.

                          Is there something else I'm supposed to be doing other than loading the "v4l" module?

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                          • #14
                            Originally posted by RealNC View Post
                            I have a TV card. I just enabled the v4l module in my xorg.conf. When starting X, I only get a blank screen and the system freezes. Need to reboot though SysRq.

                            Is there something else I'm supposed to be doing other than loading the "v4l" module?
                            The existing xf86-video-v4l driver only supports v4l1 devices which have been deprecated in the kernel for a while and were removed in 2.6.38 IIRC. You need to use the new version with v4l2 support that was recently posted on the xorg ML, and you'll need a gpu X driver that supports the Xv offscreen images and putvideo functions. Very few drivers support these. You'll also need an app like xawtv to actually take advantage of the v4l Xv interface provided by xf86-video-v4l; it won't just work with any tv viewing app.

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                            • #15
                              It proves what we already know

                              Proronix is little more than an RSS syndicator

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