[Gridflow-dev] problems with videodev

Mathieu Bouchard matju at artengine.ca
Wed Mar 28 18:27:12 EDT 2007

On Wed, 28 Mar 2007, Alexandre Castonguay wrote:

> 'mmap' is enabled by default?

Since 2002, or maybe 2001.

>  The default 'bttv' button in the last version of [#camera] was helpful, 
> why was it removed?

I don't know, it was next to a 'pwc' button which was selecting 
'colorspace YUV420P' and enabling the automatic use of [#yuv_to_rgb], and 
those options don't exist anymore, because their handling is automatic, 
much faster, and more featureful.

That said, you could do:

{channel 1}
[#camera 0]

where {} is a messagebox. Note that the argument of [#camera] for 
auto-open was added at the same time as the 'bttv' button was removed.

In the future, [#camera 0, channel 1] will work, but not now. It requires 
some upgrading of the [args] class.

> [VideoPicture] brightness=32768 hue=32768 contrast=33791 whiteness=0
> depth=24 palette=RGB24\;
> palette 4 supported

palette 4 is RGB24 (as stated in /usr/include/linux/videodev.h) and is one 
of the 3 palettes supported by GridFlow. RGB565 (palette 3) was added last 
month because of some different chips that are also bttv but don't support 
RGB24 (such as the cards that you have and that I don't).

> error: ioctl VIDIOCPWCGAWBSPEED: Invalid argument
> error: ioctl VIDIOCPWCGAWBSPEED: Invalid argument
> error: ioctl VIDIOCPWCGAWB: Invalid argument
> error: ioctl VIDIOCPWCGAWB: Invalid argument
> error: ioctl VIDIOCPWCGAWB: Invalid argument

This is PWC-specific functions. I don't really know how to detect PWC.

> error: ArgumentError: mmap: Invalid argument 
> format/videodev.c.fcs:321:in `void FormatVideoDev::alloc_image(int, 
> Ruby*)'

Could this be related to a recent post on the video4linux mailing-list 
about the size of mmap allocations on very recent kernels? I don't know.

> (select 'transfer read') :
> transfer read
> error: ArgumentError: error reading: Input/output error

Most drivers only support mmap mode. This includes the bttv driver.
It shouldn't segfault (segfaults are always bugs).

  _ _ __ ___ _____ ________ _____________ _____________________ ...
| Mathieu Bouchard - tél:+1.514.383.3801 - http://artengine.ca/matju
| Freelance Digital Arts Engineer, Montréal QC Canada

More information about the Gridflow-dev mailing list