On 02-Jun-01 Gerd Knorr wrote:
> Nemosoft Unv. wrote:
>> but I was talking about what happens if the buffers
>> still get full;
>
> Then your box is to slow for video capture. Specifying the frame rate
> you want capture might help in this case[1]. For bttv this would'nt
> make a big difference, but with USB hardware which might have to
> post-process video data (uncompress due to the limited bus bandwidth)
> this should help a bit as you avoid processing data which will be
> dropped by the application anyway ...
>
>> drop the last or the oldest frame?
>
> Whichever is less work for the driver, i.e. probably drop the last one.
>
> Gerd
>
> [1] Hmm, no v4l2 ioctl for this yet. Add one?
Yes please; this would be great for certain webcams. (though there are
others, like the CPiA cam, who don�t have a fixed framerate at all)
There is mention of an interval setting in VIDIOC_G_PARM/VIDIOC_S_PARM
(which is just the reciproke of a framerate). However, I think that is a
very obscure place to put it. I�d rather suggest the following:
- add a flag to v4l2_capability.flags: V4L2_FLAG_VARFPS (VARiable Framerate)
- either add a an ioctl (VIDIOC_S_FPS), or stick it into the v4l2_pix_format
structure and other ascociated structs.
- Nemosoft
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