How to get D1 chroma dataformat?

Hi

I using RDK4.0, I can get the video frame, and display is ok.

But sometimes(for example, when I move camera to context color plane), I got video with noise.

Is frame data convert cause this problem? In SCD, i process 420.

So how should I do to judge current chroma format is YUV420 or not?

Thanks.