Frame rate in the VUI constraints format specific or generic?

The current frame rate reads as follows:

the timing information may be present. If the timing information is present, i.e. the value of vui_timing_info_present_flag is set to 1, then the values of vui_num_units_in_tick and vui_time_scale shall be set according to the frame rates allowed for each operation point.

This makes this normative statement ambiguous in terms of conformance.

The conformance validation can be interpreted as :

• The values of vui_num_units_in_tick and vui_time_scale can be any values allowed by all operation points in the VOPS specification. This would make the VUI constraint generic and not specific to one operation point.
• The values of vui_num_units_in_tick and vui_time_scale can only be the values allows by the operation point being validated. This makes the VUI constraint operation point specific and the validation check is different for each operation point.
• The value of vui_num_units_in_tick and vui_time_scale can only the value of the actual signal that is in the bitstream. In that case, the validation check expects only a given value that is only known of the signal information is provied.

The VUI constraint should be self0contained and be implementable regardless of external factors which is the case for all of them except this frame rate constraint.

Therefore, I would suggest changing the text as follows:

• Remove normative constraints on vui_num_units_in_tick and vui_time_scale.
• Change the text as a note

Original text:

• the timing information may be present. If the timing information is present, i.e. the value of vui_timing_info_present_flag is set to 1, then the values of vui_num_units_in_tick and vui_time_scale shall be set according to the frame rates allowed for each operation point.

New text:

NOTE: When the timing information present, the values of vui_num_units_in_tick and vui_time_scale are expected to be consistent with the frame rates allowed for each operation point and with the timing information signalled at the system level.