h264qp - A script to analyze h264 qp at macroblocks level via ffmpeg and ffprobe

[hellgauss]

I wrote a small cpp script to analyze qp values at macroblocks level via ffmpeg and ffprobe, organized per frame type ( K/I , P , B ). Results are in agreement with the x264 log at the end of encoding (sometimes average framesize is a little bit different). The motivation is to provide the same info on QP as the well known avinaptic, but with more accuracy.

This is an example of output

TOT:
N : 109201
N/TOT : 100.000000 %
Total Size : 1137524780
Total Size/TOT : 100.000000 %
Average Size : 10416.798198
AVERAGE QP : 28.333866
StdDev (frames) : 4.429616
StdDev (MB) : 6.219143

B:
N : 79928
N/TOT : 73.193469 %
Total Size : 310997300
Total Size/TOT : 27.339826 %
Average Size : 3890.968121
AVERAGE QP : 28.844389
StdDev (frames) : 4.685202
StdDev (MB) : 6.422568

P:
N : 28799
N/TOT : 26.372469 %
Total Size : 776058630
Total Size/TOT : 68.223448 %
Average Size : 26947.415882
AVERAGE QP : 27.026055
StdDev (frames) : 3.186714
StdDev (MB) : 5.347749

K+I:
N : 474
N/TOT : 0.434062 %
Total Size : 50468850
Total Size/TOT : 4.436725 %
Average Size : 106474.367089
AVERAGE QP : 21.706530
StdDev (frames) : 3.186385
StdDev (MB) : 5.063920

K:
N : 450
N/TOT : 0.412084 %
Total Size : 48814460
Total Size/TOT : 4.291288 %
Average Size : 108476.577778
AVERAGE QP : 21.804706
StdDev (frames) : 3.079572
StdDev (MB) : 5.008669

I:
N : 24
N/TOT : 0.021978 %
Total Size : 1654390
Total Size/TOT : 0.145438 %
Average Size : 68932.916667
AVERAGE QP : 19.865722
StdDev (frames) : 4.374115
StdDev (MB) : 5.701641

P+B:
N : 108727
N/TOT : 99.565938 %
Total Size : 1087055930
Total Size/TOT : 95.563275 %
Average Size : 9998.031124
AVERAGE QP : 28.362758
StdDev (frames) : 4.412535
StdDev (MB) : 6.208241

Consecutive B-Frames (number of B-Frames in each group) :
1 : 2151 ( 2.691172 % )
2 : 3404 ( 4.258833 % )
3 : 74373 ( 93.049995 % )


Optionally it also outputs detailed per-frame statistisc as follows.
First row = total number of frames
Then, for each frame, the following are reported
[Frame Type] [Frame Size] [Frame position] [Average QP of the frame] [Macroblock QP StdDev of the frame]
109201
K 99565 0 17.639706 5.942646
B 81 100109 17.125000 1.452369
B 89 100020 17.477451 2.297053
B 72 100190 20.386029 2.292464
P 455 99565 20.032475 4.160982
B 73 103057 19.386029 2.292464
B 76 103130 17.248162 1.913333
P 2795 100262 23.354657 5.087658
B 92 103528 17.984069 2.674038
B 109 103419 18.191912 3.457931
B 66 103620 33.000000 0.000000
P 213 103206 18.170956 3.413506
B 73 104318 31.788603 1.768125
P 632 103686 20.997917 4.652969
I 108528 104391 19.261397 4.447370
B 67 213822 25.000000 0.000000
B 88 213734 21.337010 1.027634
B 67 213889 25.000000 0.000000
P 815 212919 19.608701 2.853781
B 69 215874 23.000000 0.000000
B 70 215943 18.012745 0.225428
P 1918 213956 25.711029 4.187233
B 83 216932 20.799877 0.821151
P 919 216013 24.768873 5.223346
B 87 217555 22.476348 1.807915
P 540 217015 25.545711 4.772148
I 111822 217642 22.179657 4.503248
B 67 373128 29.000000 0.000000
B 13819 359309 30.065196 5.149497
...etc...

The script basically launches the command

ffmpeg -hide_banner -loglevel error -threads 1 -i inputFile -map 0:V:0 -c:v copy -f h264 pipe: | ffprobe -threads 1 -v quiet -show_frames -show_streams -show_entries frame=key_frame,pkt_pos,pkt_size,pict_type -debug qp -i pipe:

and parses stdout and stderr. More info in the readme.txt

It consists in only one .cpp file so it can be easily be compiled. E.g. in Embarcadero Dev-ccp it only requires the flag -std=c++17 to be added to compiler options. The script is provided "as is" without any warranty, fell free to copy, modify and distribute it.

EDIT: just created my first page on github
https://github.com/HG3112/h264qp

[tormento]

Please evaluate to create a similar one for hevc.

[hellgauss]

That's not so easy. Unfortunately the debug qp flag does not work for hevc decoder, and it will probably not be implemented.

This is a 7 years old "wish" ffmpeg ticket

https://trac.ffmpeg.org/ticket/6637

I managed to parse per-slice (per-frame) qp informations on hevc stream using "-bsf:v trace_headers" trying to grab approximated info. It works well for videos coded at constant quantizer with "--qp" x265 options. However, with --crf encodings it gives completely wrong results. I assume that hevc can store a lot of informations at macroblocks level to optimize encoding.

Another approach I tried to follow is the usage of "videoparse.dll" from this repository

https://github.com/Telecommunication-Telemedia-Assessment/bitstream_mode3_videoparser

However I've not been able to compile it under windows, and it seems that it is a challenge even for skilled programmers. I only have some little experience using Visual Studio Community Edition, I'm not a Software Developer.

[shae]

Thanks.

I wonder why MediaInfo doesn't support scanning a file for detailed stats.