Copied from https://gitlab.freedesktop.org//gstreamer/gst-plugins-bad/-/merge_requests/1215
This reverts commit 43006110.
The assumption was that:
There is nothing in the spec that state that framerate is not valid in that case.
However, when looking at the speci (section E.2.1), it clearly states that:
fixed_frame_rate_flag equal to 1 indicates that the temporal distance between the HRD output times of any two consecutive pictures in output order is constrained as follows. fixed_frame_rate_flag equal to 0 indicates that no such constraints apply to the temporal distance between the HRD output times of any two consecutive pictures in output order. When fixed_frame_rate_flag is not present, it shall be inferred to be equal to 0.
Moreover, the process for calculating DeltaTfiDivisor is clearly conditioned to this flag being set to 1:
When fixed_frame_rate_flag is equal to 1 for a coded video sequence containing picture n [..]
There is no provision for the value of DeltaTfiDivisor when fixed_frame_rate_flag is 0.