[FFmpeg-devel] [PATCH 01/24] avcodec: add color_range to AVCodec struct

[Vittorio Giovara]

--

On 5/1/2018 4:39 PM, Paul B Mahol wrote:
> Signed-off-by: Paul B Mahol <onemda at gmail.com>
> ---
>  libavcodec/avcodec.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
> index fb0c6fae70..3a8f69243c 100644
> --- a/libavcodec/avcodec.h
> +++ b/libavcodec/avcodec.h
> @@ -3433,6 +3433,7 @@ typedef struct AVCodec {
>      uint8_t max_lowres;                     ///< maximum value for lowres supported by the decoder
>      const AVClass *priv_class;              ///< AVClass for the private context
>      const AVProfile *profiles;              ///< array of recognized profiles, or NULL if unknown, array is terminated by {FF_PROFILE_UNKNOWN}
> +    const enum AVColorRange *color_ranges;  ///< array of supported color ranges by encoder, or NULL if unknown, array is terminated by AVCOL_RANGE_UNSPECIFIED
>  
>      /**
>       * Group name of the codec implementation.
> 

While I appreciate this effort to remove the year-long deprecated J-pixel
format, I have a feeling that this is not the right way to do it.

I have no doubt that the code presented here works as expected, however
adding YetAnotherField to the AVCodec structure is a slippery road. Namely
only adding color range as an extra feature of the pixel format is incomplete.

We should add every other single color parameter in this structure, insert
the appropriate conversion filters (which swscale is not fully able to
produce) and handle correct format negotiation across the chain, which is
not exactly trivial (ie. which color space should be favoured? which one has
a larger gamut? and so on).

This creates a precedent that, I think, is bad API-wise and user-wise.
I would rather keep the J-format around than creating a years long user-facing
problem. Additionally having this field (or these fields if we are to include
the other color properties) around makes the intrisic problem even harder
to properly fix.

I am aware that the goal of this patchset is not to properly support all
color conversion properties, and it's just to being able to drop the J-formats,
but I hope that this feedback will give a larger picture of the problem
involved, that it will help you in making the right decision about this set.

Regards
Vittorio