On Wed, Sep 18, 2019 at 11:37 AM Hello Vectronic
<hello.vectro...@gmail.com> wrote:
>
> Hello,
>
> I need to implement support for reading and writing ICC profiles which can be
> stored in MOV/MP4 sample descriptor colour information.
>
> The relevant extract from the ISO standard is:
>
> class ColourInformationBox extends Box('colr'){
> unsigned int(32) colour_type;
> if (colour_type == 'nclx') /* on-screen colours */
> {
> unsigned int(16) colour_primaries;
> unsigned int(16) transfer_characteristics;
> unsigned int(16) matrix_coefficients;
> unsigned int(1) full_range_flag;
> unsigned int(7) reserved = 0;
> }
> else if (colour_type == 'rICC')
> {
> ICC_profile; // restricted ICC profile
> }
> else if (colour_type == 'prof')
> {
> ICC_profile; // unrestricted ICC profile
> }
> }
>
> At the moment the code only supports nclc/nclx colour type in:
>
> libavformat/mov.c => mov_read_colr()
> libavformat/moveenc.c => mov_write_colr_tag()
>
> Support for ICC profile is implemented on a per frame basis in
> AVFrameSideDataType.AV_FRAME_DATA_ICC_PROFILE. This is used by the PNG, WEBP
> and MJPEG codec implementations. The ICC profile in this scenario is treated
> as an opaque octet buffer. I don't believe this is relevant to my use case as
> the colour information within the MOV/MP4 sample descriptor relates to the
> entire stream and is not used on a per-frame basis.
>
> My thinking is to implement support for ICC profile in a similar way that
> color_range, color_primaries etc. are currently handled:
>
> 1. Store the ICC profile as an opaque octet buffer stored in an
> AVCodecParameters struct value:
>
> uint8_t *icc_profile_data;
> int icc_profile_size;
>
Something like this has no place in AVCodecParameters, which is
intentionally kept simple and easy. It should be stream-global
side-data, similar to the frame side data, just on a stream level,
which is already a concept we have, so it should be easy to fit it in
there.
- Hendrik
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