MJPEG is slow, suggest YUYV in docs/config

[strayr]

Is your feature request related to a problem? Please describe

Some webcams are painful slow, crowsnest is brilliant for pi cam and on raspberry pi hardware. On other platforms with generic USB webcams, ustreamer in mjpeg mode is just painful. This reddit thread describes the pain https://www.reddit.com/r/klippers/comments/18v8cwh/extremely_low_fps_on_crowsnest_webcam/

I was particularly confused when i moved a webcam from one thin client to another and suddenly it went from a massive framerate to near unusable.

Describe the solution you'd like

Suggest users try

custom_flags: --format=YUYV

if they are experiencing very slow framerates with usb webcams. This could be in the docs, or as a comment in the config file, the latter is more likely to be helpful. Seriously, just something like this will save many users screaming.

#custom_flags: --format=YUYV         # try this if you are experiencing very low framerates with a usb webcam using ustreamer.

Describe alternatives you've considered

Buying a raspberry pi and a pi cam - really expensive, i have usb webcams and thin clients that otherwise work.

Additional information

No response

[mryel00]

You are right, I saw that sometimes in our support forum too. I'm currently rewriting some parts of the docs for v5, so I will add this under common problems.