conversion from stereo stream to mono stream #276

I'm trying to write a code that reads a video/audio file with multiple audio channels and extracts only one channel and write it to another file.

My main problem is when I initialize a new audio frame using:
f = av.audio.frame.AudioFrame(format=...,layout=..., samples=...)
I get NotImplementedError

And in the same time, I cannot update the original frame calling Update_buffer method with half of the samples since I will get something like "ValueError: got 2048 bytes; need 4096 bytes". And of course, also I cannot delete panels !!!

I was searching in the API documentation for anything that may help but I couldn't. Can you give me an advice about this