Re: Journey in cheese code;

[Filippo Argiolas <fargiolas gnome org>]

On Wed, Feb 24, 2010 at 3:28 PM, Nicolas Bertrand <nico inattendu org> wrote:
> Hi,

Hey,

> I played a lot with cheese 2.29.0, the libcheese is awesome ;-) . And
> the test programs very interesting to understand the Lib.

Great :)

> The possibility of use CheeseWdiget, CheeseCamera or
> CheeseCameraDeviceMonitor very useful also.
> I view that cheese does not use the webcam framerate info. It can be
> useful to play with webcam framerate for CPU load. Webcam have framerate
> range, with a lowest framerate CPU load go considerably down.

I removed it given that we were not using anything but the maximum anyway.
Did you experience any CPU load difference changing the framerate in
v4l2src itself?
I can run the following pipeline here with different framerates and
there is no noticeable difference in speed load, I'd say 1% difference
between 9/1 and 30/1 fps.
gst-launch-0.10 v4l2src ! video/x-raw-yuv, framerate=30/1 ! fakesink

So I think the cpu load becomes important when you pass those frames
through other processing elements and you're right, decreasing
framerate can be useful for that. But, it can easily be done with
videorate.
You set the src framerate to the maximum[1] available and then drop
some frames setting the framerate caps after videorate.
This way you can still control the framerate in your pipeline but you
can avoid the whole hassle of enumerating and parsing supported
framerates. You just have the maximum one and videorate does the rest
with minimal overhead.

Note: if anyone in the list thinks I'm missing anything and the
previous paragraph is totally crack please talk now :)

> So, the libcheese lib is enough I think, and my webcam detection lib
> unuseful.
>
> So I go to start on the python bindings.
>
> See you soon for more info on cheese journey

Amazing, keep us updated!

Filippo

1. Well, we currently set the maximum available under 30 fps. That's
because there are some webcams that advertise 100fps or more but don't
work really work when you ask them that rate and, by the way, I don't
really think human eye can perceive any difference between 30 and 100
frames per second. Anyway I plan to make that parameter configurable
sooner or later.