When I set compositor's parameters, the camera has Probability will go wrong

[uil uil]

Hello

I made a program, which the structure is similar to this:

appsrc   ->  (some operations) ->  queue  ->  |
v4l2src1 -> (some operations) ->  queue  -> |  -> compositor ->
(some operations) -> fbdevsink
v4l2src2 -> (some operations) ->  queue  -> |

("some operations" include videoconvert,videorate,videobox and so on )

and  I operation the compositor by set property like xpos,ypos,alpha
and zorder,
to make PIP , single mode  and so on.

It work good in the begin, But v4l2src1 and v4l2src2 has Probability will
go error like this:

Error v4l2src1: gst-stream-error-quark: Internal data stream error. (1),
gstbasesrc.c(3072): gst_base_src_loop ():
/GstPipeline:main/GstBin:bin10/GstV4l2Src:gstv4l2src1:
streaming stopped, reason not-negotiated (-4)

 I think the buffer between compositor and camera'src  is stuck, but I have
no idea how to debug.

Can anyone help? Thank you!
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