RE: Cheese Webcam Booth Frame Rates

[Alexey Fisher <bug-track fisher-privat net>]

Am Freitag, den 29.04.2011, 01:39 -0700 schrieb John Selbie:
> 
> The Lifecam Cinema camera can't do 30fps at YUV or RGB.  There's just not enough USB bandwidth available.  It doesn't even support it when you programatically enumerate it's formats.
> 
> But it can do higher frame rates if it's configured to use it's MJPG format.   Requires the jpg filter to decode at that rate.  Uses more CPU.
> 
> 
> Lifecam cinema has following formats and max frame rates:
> 
> YUY2 at 30fps for multiple formats from 160x120 up to 640x480.
> YUY2 at 7.5fps for 800x448, 960x544, and 1280x720
> YUY2 at 10fps for 1280x800
> MJPG at 30fps for all formats from 160x120 all the way up to 1280x800.
> 
> Not sure how Cheese builds the gstreamer graph, but the developers could consider giving priority to MJPG formats over YUV or RGB when the frame rate is higher in that size.

The quality and speed of webcams built in jpeg encoder is different,
mostly it is not so good. Some webcams can't keep 30fps on  big
resolution, or need to prefer worst jpeg quality in favor if better
encoder speed.

IMHO this is why RAW stream should be preferred for cheese.

- second argument will be cpu usage. How strong should be CPU to encode
1280x800 at 30 fps? Most of modern CPU will have some problems with it.
If you also add jpeg decodig (sure it is not a big problem) and audio
encoding?

- do you really need 30 fps? Youtube seems to re encode videos to 25fps.
Even with 20 fps most people will not see any difference.

- by default most webcams use aperture priority, also variable frame
rate. With normal light you will get about 15fps, even if 30fps is
choiced . Only if you get more light or choice shooter priority you'll
get 30fps.

Cheese can't make a correct choice to what you need and what your pc
really can.