Fix webcam on Arch Linux

Tested on a quelima sq11.

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# ERRO
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$ ffmpeg -f v4l2 -video_size 640x480 -i /dev/video0 -c:v libx264 -preset ultrafast webcam.mp4
/dev/video0: Input/output error




Try setting the quirks parameter to 2 before plugging your webcam (either 
with 'modprobe uvcvideo quirks=2' if the driver is not already loaded, or 
with 'echo 2 > /sys/modules/uvcvideo/parameters/quirks' if the driver is 
already loaded).

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# Changing on a module
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you can change the behaviour of many kernel-modules by passing some parameters.
you can get a list of all available module parameters with the modinfo command:

# modinfo uvcvideo

shows that there is a "quirks" parameters, which can be used. looking at the faq you posted, it seems that the quirks are really a bitfield, so if you want to enable multiple quirks, you have to add the numbers.

first unload the driver (obviously you must not use it when doing so):

# rmmod uvcvideo
then re-load it with the quirks parameter. assuming you want to enable both UVC_QUIRK_FIX_BANDWIDTH (which has the hex-value 0x80, which is 128 in decimal) and UVC_QUIRK_RESTRICT_FRAME_RATE (which is 0x200 thus 512) you would use a quirks value of 640 (which is 128+512 resp. 0x200|0x80):

# modprobe uvcvideo quirks=2


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# Permanent change on a module
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Add it to /etc/modprobe.d/uvcvideo.conf:

# fix bandwidth issue for quelima SQ11
options uvcvideo quirks=2




refernences:
https://sourceforge.net/p/linux-uvc/mailman/message/29832729/
https://stackoverflow.com/questions/25619309/how-do-i-enable-the-uvc-quirk-fix-bandwidth-quirk-in-linux-uvc-driver
https://wiki.archlinux.org/index.php/Webcam_setup