Re: [libcvd-members] Problems with V4L2 and gspca driver

[E. Rosten]

On Sun, 16 Aug 2009, Daniel Tabares Fernaud wrote:

> Hi
> Fist of all, sorry for my english
>
> I have a problem using V4l2 cameras.
>
> I have two Creative WebCam Vista (lsusb ID 041e:405f).
> When I used Ubuntu 8.04, i haven't problems using v4l1 and ov51x-jpeg driver. 
> But this driver actually haven't support for Ubuntu 9.04 kernel (2.6.28-11. 
> Actually, I use this distribution, and I use the gspca driver, ov519 module 
> (http://linuxtv.org). The driver works well in most applicatons (cheese, for
> example), but in the example application included in libcvd, 
> "video_play_source", executed with the following parameters:
>
> ./video_play_source v4l2:[verbose]///dev/video0
>
> its output shows:
>
> V4L2Client: verbose operation. Initializing
> V4L2Client: Querying capabilities.
> V4L2Client:    driver: ov519
> V4L2Client:    card: Creative WebCam Vista
> V4L2Client:    bus_info: 0000:00:13.3
> V4L2Client:    version: 131840
> V4L2Client:    capabilities: 0x5000001
> V4L2Client:                 V4L2_CAP_VIDEO_CAPTURE        = 1
> V4L2Client:                 V4L2_CAP_VIDEO_OUTPUT         = 0
> V4L2Client:                 V4L2_CAP_VIDEO_OVERLAY        = 0
> V4L2Client:                 V4L2_CAP_VBI_CAPTURE          = 0
> V4L2Client:                 V4L2_CAP_VBI_OUTPUT           = 0
> V4L2Client:                 V4L2_CAP_SLICED_VBI_CAPTURE   = 0
> V4L2Client:                 V4L2_CAP_SLICED_VBI_OUTPUT    = 1
> V4L2Client:                 V4L2_CAP_RDS_CAPTURE          = 0
> V4L2Client:                 V4L2_CAP_VIDEO_OUTPUT_OVERLAY = 0
> V4L2Client:                 V4L2_CAP_TUNER                = 1
> V4L2Client:                 V4L2_CAP_AUDIO                = 0
> V4L2Client:                 V4L2_CAP_RADIO                = 0
> V4L2Client:                 V4L2_CAP_READWRITE            = 1
> V4L2Client:                 V4L2_CAP_ASYNCIO              = 0
> V4L2Client:                 V4L2_CAP_STREAMING            = 1
> V4L2Client: Requested format: RGB3
> V4L2Client: Enumerating formats.
> V4L2Client:    Index  FourCC     Flags    Description
> V4L2Client:        0   JPEG   0x00000001  JPEG
> V4L2Client: Selected format: None
> V4L2Client: Getting format (VIDIOC_G_FMT)
> V4L2Client:    size: 640x480
> V4L2Client:    format: JPEG
> V4L2Client:    field flag: 1
> V4L2Client:    bytes per line: 640
> V4L2Client:    image size: 115790
> V4L2Client:    colourspace: 7
> V4L2Client: Setting format (VIDIOC_S_FMT)
> V4L2Client:    size: 640x480
> V4L2Client:    format: None
> V4L2Client:    field flag: 0
> V4L2Client:    bytes per line: 640
> V4L2Client:    image size: 115790
> V4L2Client:    colourspace: 7
> V4L2Client: Getting format (VIDIOC_G_FMT)
> V4L2Client:    size: 640x480
> V4L2Client:    format: JPEG
> V4L2Client:    field flag: 1
> V4L2Client:    bytes per line: 640
> V4L2Client:    image size: 115790
> V4L2Client:    colourspace: 7
> Error: V4LBuffer: "V4L2: Requested format not supported" ioctl failed on 
> /dev/video1: Invalid argument
>
> The VideoBuffer is VideoBuffer<Rgb<byte>>, and the camera apparently only 
> support JPEG format.
>
> Has the problem any solution?

None of the solutions are especially pretty, but you could make it work. 
At the moment libCVD won't generally do any automatic conversions on live 
image capture, for efficiency reasons. This has been relaxes a bit 
recently for cameras which hand back JPEG images (not v4l cameras, 
though).

The best solution would probably be to hack v4l2 buffer so it will perform 
JPEG decoding of the image automatically, and return the image data as if 
it was a RGB or GREY image.

To decode the data, you could just place an istringstream around it and 
load from the stream with img_load.

-Ed



--
(You can't go wrong with psycho-rats.)(http://mi.eng.cam.ac.uk/~er258)

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