At 2018-09-05 19:52:23, "Mark Thompson" <s...@jkqxz.net> wrote:
>On 05/09/18 08:19, Huiwen Ren wrote:
>> At 2018-09-05 08:46:18, "Mark Thompson" <s...@jkqxz.net> wrote:
>>> On 03/09/18 03:42, hwren wrote:
>>>> Signed-off-by: hwren <hwr...@126.com>
>>>> ---
>> [...]
>>>> +
>>>> + int i_lcurow_threads;
>>>> + int i_initial_qp;
>>>> + int preset_level;
>>>> + int intra_period;
>>>
>>> There is a common option AVCodecContext.gop_size (-g) which should probably
>>> be used rather than inventing a new private option with the same meaning.
>>
>> intra_period in xavs2 seems not equals to gop_size in ffmpeg, intra period
>> here is calculated by (actul_intra_period/gop_size).
>
>I'm not entirely sure what you mean here. Let me try to explain what I think
>this doing, please correct me if I'm getting anything wrong.
>
>The intra frames sent in a stream are arranged something like (xxx
>representing any sequence of non-intra frames):
>
>IDR xxx I xxx I xxx I ... I xxx IDR
>
> | <-A-> | <-A-> | <-A-> | ... | <-A-> |
> ^ ^ B instances of A ... ^
> | <---------------- C ----------------> |
>
>Both I and IDR frames are recovery points.
>
>Then, with your naming:
>
>A = GOP size
>B = Intra period
>C = what you've called "actul intra period" above and in the docs
>
>and A * B = C
>
>Only being able to set B, though, seems insufficient to control this? Any one
>variable is determined by the other two, but you need at least two of them.
>
You are right. Sorry, I may mistakenly assume the meaning of gop_size. It
should be the "A" above and I've replaced intra_period with AVContext->gop_size.
>
>Aside: the libmfx code calls the B variable "IDR interval", which I think is
>slightly clearer (see
><http://git.videolan.org/?p=ffmpeg.git;a=blob;f=libavcodec/qsvenc_h264.c;h=06fa0ebf065b2426b9f77aeaef3a20f41466ee1c;hb=HEAD#l109>).
>
>>>> + if (avctx->bit_rate > 0) {
>>>> + cae->api->opt_set2(cae->param, "RateControl", "1");
>>>> + av_strlcatf(str_TBR, sizeof(str_TBR), "%d", avctx->bit_rate);
>>>> + cae->api->opt_set2(cae->param, "TargetBitRate", str_TBR);
>>>> + }
>>>
>>> What happens if there is no bitrate target? Some sort of constant-quality
>>> mode? Are there any parameters for that?
>>
>> Rate control in xavs2 will only work if given bit_rate and the speed(preset)
>> level is used to control quality.
>
>Please do correct me if this is wrong, but I thought the speed/preset value
>was the encoding-time against quality tradeoff? When bitrate is not set I
>would expect there to be a parameter for the size against quality tradeoff as
>well (e.g. a fixed QP value that will be used for every frame - in
>AVCodecContext this generally maps to global_quality, though not all encoders
>use it).
Sorry again. It should be the i_initial_qp which could control the initial qp
for first frame, instead of speed_level.
Thanks for correction,
Huiwen Ren
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