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...e3_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.