[FFmpeg-devel] [PATCH 4/4 v2] avcodec/av1: signal the presence of Film Grain in the decoder context

[James Almer]

On 8/16/2021 1:45 PM, James Almer wrote:
> On 8/16/2021 1:35 PM, Lynne wrote:
>> 16 Aug 2021, 18:24 by jamrial at gmail.com:
>>
>>> Signed-off-by: James Almer <jamrial at gmail.com>
>>> ---
>>>   libavcodec/av1dec.c | 5 +++++
>>>   1 file changed, 5 insertions(+)
>>>
>>> diff --git a/libavcodec/av1dec.c b/libavcodec/av1dec.c
>>> index 1dda0f9160..a69808f7b6 100644
>>> --- a/libavcodec/av1dec.c
>>> +++ b/libavcodec/av1dec.c
>>> @@ -575,6 +575,11 @@ static int 
>>> set_context_with_sequence(AVCodecContext *avctx,
>>>   break;
>>>   }
>>> +    if (seq->film_grain_params_present)
>>> +        avctx->properties |= FF_CODEC_PROPERTY_FILM_GRAIN;
>>> +    else
>>> +        avctx->properties &= ~FF_CODEC_PROPERTY_FILM_GRAIN;
>>> +
>>>   if (avctx->width != width || avctx->height != height) {
>>>   int ret = ff_set_dimensions(avctx, width, height);
>>>   if (ret < 0)
>>>
>>
>> Why do we need to signal whether decoders support it or not? Is it in 
>> case
>> we have decoders which don't support applying film grain yet can 
>> export it?
> 
> This is signaling the presence of film grain regardless of how it's 
> handled, not that the decoder supports it, in a way the library user can 
> query.

That being said, of course only decoders that support handling film 
grain in some form are going to set this flag to being with. The point 
is being able to do what i described below.

> 
> If a decoder applies film grain instead of exporting it as side data, 
> there's nothing currently letting the library user know it's there at all.
> 
>> Or is it to perhaps to implicitly signal which types of film grain 
>> clients can get
>> in case they want to export film grain and apply it themselves, so 
>> they can
>> disable film grain exporting if they can't apply the type that the 
>> decoder outputs
>> yet?