On 06/09/18 14:46, Huiwen Ren wrote:
> At 2018-09-06 08:43:05, "Mark Thompson" <[email protected]> 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
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