Incorrect encoding bit rate

[Renzzauw]

Hi!

I'm initializing the VPF encoder as follows:

output_width, output_height = output_resolution
enc_args = {
    'codec': 'h264',
    'preset': 'P4',
    's': f"{str(output_width)}x{str(output_height)}",
    'tuning_info': 'high_quality',
    'bitrate': '10M',
    'profile': 'high',
    'cbr': '1',
    'fps': fps,
}

video_encoder = nvc.PyNvEncoder(enc_args,
                                gpu_id=gpu_device,
                                format=nvc.PixelFormat.NV12)

After some experimenting with FFmpeg & hwaccel CUDA I came to the encoding presets as defined above to be suitable for my application. However, when I encode a video using these settings & mux to an .mp4 container, I noticed when I use a tool like mediainfo the bit rate is far from the one I defined:

Video
ID                                       : 1
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : High@L3.1
Format settings                          : CABAC / 3 Ref Frames
Format settings, CABAC                   : Yes
Format settings, Reference frames        : 3 frames
Codec ID                                 : avc1
Codec ID/Info                            : Advanced Video Coding
Duration                                 : 7 s 942 ms
Bit rate                                 : 2 233 kb/s <------------------
Width                                    : 1 280 pixels
Height                                   : 720 pixels
Display aspect ratio                     : 16:9
Frame rate mode                          : Constant
Frame rate                               : 29.970 (29970/1000) FPS
Original frame rate                      : 29.970 (30000/1001) FPS
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Progressive
Bits/(Pixel*Frame)                       : 0.081
Stream size                              : 2.11 MiB (87%)
Codec configuration box                  : avcC

I was wondering, does my specified bit rate get overwritten when using a preset? Is this intended behavior? I also tried passing default as preset, and the bit rate of the output video is around (but not exactly) the 10 I provided. So is this a bug or am I using the encoder incorrectly?

Thanks!

[Renzzauw]

For extra context, the ffmpeg command I try to replicate with VPF is as follows:

ffmpeg -hwaccel cuda \
[...]
-map [v1out] -c:v:0 h264_nvenc -profile:v high -preset p4 -cbr 1 -tune hq -b:v:0 10M
[...]

Here v1out is my input video. I omitted most of my script since it's a bit complex and the rest is outside the scope of this issue. Hope this is useful!