> On 18 Sep 2019, at 11:09, Hendrik Leppkes <h.lepp...@gmail.com> wrote:
>
> 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
>
Thanks for the advice.
So it seems I would:
1. add a new enum value AVPacketSideDataType.AV_PKT_DATA_ICC_PROFILE
2. use av_stream_add_side_data() when reading from the MOV/MP4 in
libavformat/mov.c => mov_read_colr()
3. use av_stream_get_side_data() when writing to the MOV/MP4 in
libavformat/moveenc.c => mov_write_colr_tag()
And I think that is it..?
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