* UVC frame interval inconsistency
@ 2012-04-11 10:27 Rémi Denis-Courmont
2012-04-16 12:40 ` Laurent Pinchart
0 siblings, 1 reply; 2+ messages in thread
From: Rémi Denis-Courmont @ 2012-04-11 10:27 UTC (permalink / raw)
To: linux-media
Hello guys,
I have been reworking the V4L2 input in VLC and I hit what looks like a
weird bug in the UVC driver. I am using a Logitech HD Pro C920 webcam.
By default, VLC tries to find the highest possible frame rate (actually
smallest frame interval in V4L2), then the largest possible resolution at
that frame rate.
When enumerating the frame sizes and intervals on the device, the winner
is 800x600 at 30 f/s. But when setting 30 f/s with VIDIOC_S_PARM, the
system call returns 24 f/s. Does anyone know why it is so? Is this a
firmware bug or what?
--
Rémi Denis-Courmont
Sent from my collocated server
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: UVC frame interval inconsistency
2012-04-11 10:27 UVC frame interval inconsistency Rémi Denis-Courmont
@ 2012-04-16 12:40 ` Laurent Pinchart
0 siblings, 0 replies; 2+ messages in thread
From: Laurent Pinchart @ 2012-04-16 12:40 UTC (permalink / raw)
To: Rémi Denis-Courmont; +Cc: linux-media
Hi Rémi,
On Wednesday 11 April 2012 12:27:08 Rémi Denis-Courmont wrote:
> Hello guys,
>
> I have been reworking the V4L2 input in VLC and I hit what looks like a
> weird bug in the UVC driver. I am using a Logitech HD Pro C920 webcam.
>
> By default, VLC tries to find the highest possible frame rate (actually
> smallest frame interval in V4L2), then the largest possible resolution at
> that frame rate.
>
> When enumerating the frame sizes and intervals on the device, the winner
> is 800x600 at 30 f/s. But when setting 30 f/s with VIDIOC_S_PARM, the
> system call returns 24 f/s. Does anyone know why it is so? Is this a
> firmware bug or what?
The frame sizes and intervals returned by the uvcvideo driver during
enumeration come directly from the values advertised by the device. When you
set a frame rate using VIDIOC_S_PARM, the driver then negotiates the value
with the device, and returns the frame rate it received from the device to the
application. The device is free to adjust the frame rate (based on current
lightning conditions for instance, if auto-exposure is turned on).
--
Regards,
Laurent Pinchart
^ permalink raw reply [flat|nested] 2+ messages in thread
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2012-04-11 10:27 UVC frame interval inconsistency Rémi Denis-Courmont
2012-04-16 12:40 ` Laurent Pinchart
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