On 07/10/11 10:42, Alexey Fisher wrote:
Am 07.10.2011 10:59, schrieb Sebastian Arcus:
On 06/10/11 17:28, Alexey Fisher wrote:
On 06.10.2011 18:16, Sebastian Arcus wrote:
On 06/10/11 15:59, Alexey Fisher wrote:
On 06.10.2011 14:32, Sebastian Arcus wrote:
Hello list,
The above two cameras, which have the well known usb bandwidth bug
under
Linux don't seem to display the same problems under Windows. I've
tried
them under Windows Vista and Windows 7 32bit. I've managed to
display a
LifeCam Studio and LifeCam Cinema at the same time through separate
instances of VLC all the way to 1920x1080 for LifeCam Studio and
1280x720 for the LifeCam Cinema - which I believe are the maximum
video
resolutions for both cameras. I've forced VLC on 25fps - and the
Cinema
seems to do that. However, looking at the footage from the Studio at
maximum resolution - it looks more like 5fps.
However, what all the above means is that these cameras don't seem to
suffer from the usb bandwidth bug under Windows. I've input "mjpg"
under
chroma settings for VLC - but I can't find a way to tell for sure
if VLC
is using the mjpeg stream from the camera, or raw.
Can someone here help me push this further? Is there any way of
debugging what is happening under Windows - so that maybe the Linux
uvc
driver can be modified to get these cameras to work properly?
Any suggestions much appreciated.
Sebastian
Hi Sebastian,
Probably usb sniffing will be most correct option, but currently i'll
would not interpret usb dump.
Other option is visual test:
- Jpeg stream has lower quality, try it under linux and you will see
the
difference.
- according to frame rate the webcam controller will change
demosaicing
algorithm. Simple alorithm produce pure qualithy, and image looks like
up scaled image from smaller image. Logitech webcams use better
algorithm before 15 fps and pure after 15 fps.
- you can check frame rate by capturing some timer with milliseconds:
http://tools.arantius.com/stopwatch
Thank you Alexey. Looking at the quality of the footage - I would guess
it is not mjpeg. However, it still means that the camera is not
grabbing
all the available usb bandwidth like it does under Linux - which is
good
news.
Sebastian
Then try bandwidth quirk:
sudo rmmod&& sudo modprobe uvcvideo quirks=0x80
But reduce frame rate, 1280x720 at 30 fps will take complete bindwidth,
try 10fps if you wont to use two webcams.
Thanks Alexey.
Anybody knows if I can use VLC or some other software under windows to
view the mjpeg stream? I could then test how many cameras I can use at
the same time under Windows with mjpeg. This should tell us if the
Windows driver doesn't have any of the usb bandwidth problems which
exist under Linux for these cameras.
Sebastian
It is not a driver problem,
the webcam tell how match it need, the driver will give it. If cam tell
it need every thing we have, the driver will give it. It is defined
behavior of UVC, if device is broken, there is nothing driver can do. I
will not wonder if Microsoft will have quirks for devices it produce.
For some time i send here some jpeg patches, you can test it on your own
risk and force the bandwidth. But this patches will probably never go to
upstream.
Thanks Alexey. What I was suggesting is that, under Windows, the camera
doesn't seem to suffer from this bug - as it is possible to run two of
them at the same time. I don't know how this is accomplished, I don't
know if the Windows driver makes use of special signalling to stop the
camera from asking for all the available usb bandwidth. I was only
thinking that if it would be possible to find out how the camera is
"convinced" to not asked for full bandwidth under Windows - maybe that
can be replicated in the uvc driver under Linux. However, I know almost
nothing about the intricacies of the uvc standard and the corresponding
Linux (or Windows) implementation - that is why I was asking if there is
anyway to probe the uvc driver in Windows and find out more that way.
Many thanks,
Sebastian
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