Where is the `av.bitstream ` now?

https://github.com/isarsoft/nvenc-h264-video-reader/blob/e8f109cc728daac4c06796223abb1046468820b5/GPUVideoReader.py#L7 I see an old code above. But i can not find av.bitstream in pyav 10.0. So where is it now? What can i use what to replace it?