Re: Changing the frame rate while streaming, legal or not ?

[Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxx>]

On Mon, 31 Dec 2007 02:44:55 -0800
Brandon Philips <brandon@xxxxxxxx> wrote:

> On 01:27 Fri 07 Dec 2007, Laurent Pinchart wrote:
> > are applications allowed to change the frame rate while streaming ? I haven't 
> > found much about this in the V4L2 spec.
> 
> Which ioctls are you thinking of?  I assume VIDIOC_S_PARM and
> VIDIOC_S_STD?
> 
> I think it should be legal for a driver to return EBUSY on S_STD/S_PARM
> while streaming.  A number of other S_* calls are allowed to do this
> while I/O is in progress:
> 
> - VIDIOC_S_AUDIO
> - VIDIOC_S_INPUT
> - VIDIOC_S_OUTPUT
> - VIDIOC_S_FMT 
> 
> In general it seems that after the physical attributes of a stream
> (standard , frame rate, format) are set a driver should be able to
> return EBUSY if IO is running.
> 
> > USB devices do not always allow a frame rate change while streaming, as that 
> > implies raising the isochronous bandwidth. Drivers would then have to stop 
> > streaming, renegotiate the parameters and restart streaming transparently. As 
> > this would be a bit of work, I'd like to make sure this is allowed by V4L2 
> > before implementing it.
> 
> Mauro, how are you handling this in tm6000?

Generally, only mpeg capable video devices allows changing the frame rate. This
is not the case of tm6000. I suspect that ivtv devices return -EBUSY.

I don't see any troubles on returing -EBUSY in this case.

Cheers,
Mauro

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