Hi Theodore, On Monday 13 September 2010 19:17:48 Theodore Kilgore wrote: > On Mon, 13 Sep 2010, Laurent Pinchart wrote: > > On Friday 07 May 2010 20:20:38 Wang, Wen W wrote: > > > Hi all, > > > > > > I'm wondering if V4L2 framework supports dual stream video capture > > > device that transfer a preview stream and a regular stream (still > > > capture or video capture) at the same time. > > > > > > We are developing a device driver with such capability. Our proposal to > > > do this in V4L2 framework is to have two device nodes, one as primary > > > node for still/video capture and one for preview. > > > > If the device supports multiple simultaneous video streams, multiple > > video nodes is the way to go. > > > > > The primary still/video capture device node is used for device > > > configuration which can be compatible with open sourced applications. > > > This will ensure the normal V4L2 application can run without code > > > modification. Device node for preview will only accept preview buffer > > > related operations. Buffer synchronization for still/video capture and > > > preview will be done internally in the driver. > > > > I suspect that the preview device node will need to support more than the > > buffer-related operations, as you probably want applications to configure > > the preview video stream format and size. > > > > > This is our initial idea about the dual stream support in V4L2. Your > > > comments will be appreciated! > > > > You should use the media controller framework. This will allow > > applications to configure all sizes in the pipeline, including the frame > > sizes for the two video nodes. > > Hi, Wen, > > You have hit upon an old and rather vexing problem. It affects many > devices, not just your prospective one. The problem is that still mode is > supported in Linux for a lot of cameras through userspace tools, namely > libgphoto2 which uses libusb to interface with the device. But if the same > device can also do video streaming then the streaming has to be supported > through a kernel module. Thus until now it is not possible to do both of > these smoothly and simultaneously. > > As I have written both the kernel support and the libgphoto2 support for > several dual-mode cameras, I am looking into the related problems, along > with Hans de Goede. But right now I am dealing instead with a rather > severe illness of a family member. So there is not much coding going on > over here. > > What I think that both of us (Hans and I) agree on is that the kernel > modules for the affected devices have to be rewritten in order to allow > the opening and closing of the different modes of the devices, and > (perhaps) the userspace support has to take that into account as well. > There might also have to be some additions to libv4l2 in order to make it > "aware" of such devices. We have not gotten very far with this project. > Hans is quite busy, and so am I (see above). > > In spite of my present preoccupation, however, I would be very curious > about any details of your envisioned camera. For example: > > Does it use the isochronous mode for streaming and the bulk mode for > stills? Or not? There seems to be a small misunderstanding. The device Wen is working on (as far as I'm aware of) isn't a USB device. > In still mode, is it some kind of standard device, such as Mass Storage or > PTP? Or will it use a proprietary or device-specific protocol? If so, > it will clearly require a libgphoto2 driver. > > In video mode, will it use a proprietary or device-specific protocol, or > will it be a standard USB video class device? If it is proprietary, then > it will presumably need its own module, and if standard then in any > event we have to figure out how to make the two different modes to > coexist. > > If either of the still mode or the streaming video mode will use a > proprietary protocol and especially if some unknown data compression > algorithm is going to be in use, then clearly it is possible to get the > support going much earlier if information is provided. > > Hoping that this will help you and thanking you for any additional > information about the new camera. -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
