[FFmpeg-devel] [PATCH v4] pngdec: expose gAMA and cHRM chunks as side/meta data

[James Almer]

On 11/8/2017 9:25 PM, Rostislav Pehlivanov wrote:
> Signed-off-by: Rostislav Pehlivanov <atomnuker at gmail.com>
> ---
>  libavcodec/pngdec.c | 30 +++++++++++++++++++++++++++++-
>  1 file changed, 29 insertions(+), 1 deletion(-)
> 
> diff --git a/libavcodec/pngdec.c b/libavcodec/pngdec.c
> index 0d6612ccca..aef0d95819 100644
> --- a/libavcodec/pngdec.c
> +++ b/libavcodec/pngdec.c
> @@ -25,6 +25,7 @@
>  #include "libavutil/bprint.h"
>  #include "libavutil/imgutils.h"
>  #include "libavutil/stereo3d.h"
> +#include "libavutil/mastering_display_metadata.h"
>  
>  #include "avcodec.h"
>  #include "bytestream.h"
> @@ -1165,7 +1166,7 @@ static int decode_frame_common(AVCodecContext *avctx, PNGDecContext *s,
>      AVDictionary **metadatap = NULL;
>      uint32_t tag, length;
>      int decode_next_dat = 0;
> -    int ret;
> +    int i, ret;
>  
>      for (;;) {
>          length = bytestream2_get_bytes_left(&s->gb);
> @@ -1287,6 +1288,33 @@ static int decode_frame_common(AVCodecContext *avctx, PNGDecContext *s,
>                  goto fail;
>              break;
>          }
> +        case MKTAG('c', 'H', 'R', 'M'): {
> +            AVMasteringDisplayMetadata *mdm = av_mastering_display_metadata_create_side_data(p);
> +            if (!mdm) {
> +                ret = AVERROR(ENOMEM);
> +                goto fail;
> +            }
> +
> +            mdm->white_point[0] = av_make_q(bytestream2_get_be32(&s->gb), 100000);
> +            mdm->white_point[1] = av_make_q(bytestream2_get_be32(&s->gb), 100000);
> +
> +            /* RGB Primaries */
> +            for (i = 0; i < 3; i++) {
> +                mdm->display_primaries[i][0] = av_make_q(bytestream2_get_be32(&s->gb), 100000);
> +                mdm->display_primaries[i][1] = av_make_q(bytestream2_get_be32(&s->gb), 100000);
> +            }
> +
> +            mdm->has_primaries = 1;
> +            bytestream2_skip(&s->gb, 4); /* crc */
> +            break;
> +        }
> +        case MKTAG('g', 'A', 'M', 'A'): {
> +            av_dict_set_int(&p->metadata, "gamma_num", bytestream2_get_be32(&s->gb), 0);
> +            av_dict_set_int(&p->metadata, "gamma_den", 100000, 0);

You should use snprintf or the AVBPrint API to write a rational value in
the "x/y" or "x:y" form as single string entry to use with av_dict_set()
instead.
Having two metadata entries for a single rational value seems unwieldy.

See ff_tadd_rational_metadata() in tiff_common.c for an example of this
using AVBPrint.

> +
> +            bytestream2_skip(&s->gb, 4); /* crc */
> +            break;
> +        }
>          case MKTAG('I', 'E', 'N', 'D'):
>              if (!(s->pic_state & PNG_ALLIMAGE))
>                  av_log(avctx, AV_LOG_ERROR, "IEND without all image\n");
>