NVCODEC H.264 Encoder SEI pic_timing (dpb_output_delay)

Hello,

I am using latest Video Codec SDK (10.0.26) under Debian to encode live frames.
I am using standard configuration:

  • NV_ENC_PRESET_P3_GUID
  • NV_ENC_TUNING_INFO_HIGH_QUALITY
  • GOP Length / IDR period = 12
  • Frame Interval P = 3
  • 5 MBits/s with 1s of VBV buffer.

The encoded access units are valid and the generated stream is IDR P B B P B B P B B P B IDR.
But I have noticed that on the second IDR and on each IDRs after that, dpb_output_delay is 42 instead of 2 (I guess).
I have tried other GOP Lengths, and the result is also strange:

  • GOP Length = 3 -> dpb_output_delay = 60
  • GOP Length = 5 -> dpb_output_delay = 56
  • GOP Length = 18 -> dpb_output_delay = 18

What I am getting (for GOP 12) is :

Pictures       : IDR    P    B    B    P    B    B    P    B    B    P    B    IDR   P  B  B ...
CpbRemovalDelay:  0     2    4    6    8    10   12   14   16   18   20   22   24    2  4  6
DpbOutputDelay :  2     6    0    0    6    0    0    6    0    0    4    0    42    6  0  0

I do not understang this 42. Is it a bug ?
Am I missing something ?