F221 introduces a number of new OBU types including a layer configuration record. The F221 document says: > lcr_max_pic_width[ i][ j ], when present, specifies the maximum picture width for the decoded pictures associated with the extended layer j in either a global, when i is equal to 1, or a local, when i is equal to 0, LCR OBU. The value of lcr_max_pic_width[ i ][ j ] in a selected LCR OBU by an active SCR OBU in an extended layer with index j shall match the value of max_frame_width indicated in the SCR OBU. I am trying to write the specification, but I am not clear what is meant by the `max_frame_width in the SCR OBU`. What is an SCR OBU? Is this something that is going to appear in a later experiment? I have looked at the reference code and there does not seem to be any check in the code that corresponds to this. **Merge request author** @hegilmez **Proponent of F221 according to experiment tracker** @insukchong