[FFmpeg-devel] [PATCH v6 1/2] lavc, doc, configure: add libxavs2 video encoder wrapper

[Mark Thompson]

On 06/09/18 14:46, Huiwen Ren wrote:
> At 2018-09-06 08:43:05, "Mark Thompson" <sw at jkqxz.net> wrote:
>> On 05/09/18 14:38, hwren wrote:
>>> +    { "i_initial_qp"    ,   "Quantization parameter" ,                  OFFSET(i_initial_qp)    , AV_OPT_TYPE_INT, {.i64 = 34 }, 1,  63,  VE },
>>
>> If I understand what you said previously correctly, this is only used in constant-QP mode, and there it is used as the QP for every frame (not just the initial one)?
>>
>> If that's the case then it should probably not say "initial" - I would read "initial_qp" as meaning the QP used for the first frame only, so probably in modes with a bitrate target.  Maybe change it to just be "qp"?  That name is used by several other encoders, including libx264 and libxavs.
> 
> If "RateControl" is opened, the "initial_qp" will be used for the first frame and kept for all the other frames (constant-QP) and if there is no rate control, the initial_qp will only work for the first frame (xavs2 will always initial the qp for the first frame). So...maybe better with "initial"?

Oh, so it's actually being used for both cases here?  Then I think it should be two separate options to match other encoders ("initial_qp" for the bitrate-target case, "qp" or AVCodecContext.global_quality for the constant-quality case).

Relatedly, the min-QP default value seems to be applied in constant-quality mode as well, where it probably shouldn't be:

$ for i in $(seq 1 63) ; do ./ffmpeg_g -y -i in.mp4 -an -c:v libxavs2 -frames:v 1000 -initial_qp $i out-$i.avs ; done
...
$ rename 's/-(..avs)/-0$1/' out-*
$ du -b out-*
18464881        out-01.avs
18464878        out-02.avs
18464872        out-03.avs
18464872        out-04.avs
18464875        out-05.avs
18464872        out-06.avs
18464875        out-07.avs
18464873        out-08.avs
18464878        out-09.avs
18464878        out-10.avs
18464875        out-11.avs
18464878        out-12.avs
18464875        out-13.avs
18464872        out-14.avs
18464878        out-15.avs
18464875        out-16.avs
18464875        out-17.avs
18464878        out-18.avs
18464872        out-19.avs
18464878        out-20.avs
17015783        out-21.avs
15555727        out-22.avs
14176171        out-23.avs
12707758        out-24.avs
11603156        out-25.avs
10401092        out-26.avs
9392228 out-27.avs
8371627 out-28.avs
7476957 out-29.avs
6706333 out-30.avs
6025691 out-31.avs
5402430 out-32.avs
4877929 out-33.avs
4563285 out-34.avs
4081752 out-35.avs
3672218 out-36.avs
3290184 out-37.avs
2945455 out-38.avs
2637767 out-39.avs
2362608 out-40.avs
2119294 out-41.avs
1902747 out-42.avs
1710491 out-43.avs
1536269 out-44.avs
1390060 out-45.avs
1238536 out-46.avs
1122929 out-47.avs
1005188 out-48.avs
906167  out-49.avs
807448  out-50.avs
729962  out-51.avs
647092  out-52.avs
583707  out-53.avs
520264  out-54.avs
469991  out-55.avs
421588  out-56.avs
380653  out-57.avs
347411  out-58.avs
313181  out-59.avs
287456  out-60.avs
268281  out-61.avs
243882  out-62.avs
232726  out-63.avs


Thanks,

- Mark