h264: Add support for alternative transfer characterics SEI

The use of this SEI is for backward compatibility in HLG HDR systems:
older devices that cannot interpret the "arib-std-b67" transfer will
get the compatible transfer (usually bt709 or bt2020) from the VUI,
while newer devices that can interpret HDR will read the SEI and use
its value instead.

Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/libavcodec/h264_slice.c b/libavcodec/h264_slice.c
index c6309b298c..5dd01d836e 100644
--- a/libavcodec/h264_slice.c
+++ b/libavcodec/h264_slice.c
@@ -1154,6 +1154,12 @@ static int h264_export_frame_props(H264Context *h)
         a53->a53_caption_size = 0;
     }
 
+    if (h->sei.alternative_transfer.present &&
+        av_color_transfer_name(h->sei.alternative_transfer.preferred_transfer_characteristics) &&
+        h->sei.alternative_transfer.preferred_transfer_characteristics != AVCOL_TRC_UNSPECIFIED) {
+        h->avctx->color_trc = cur->f->color_trc = h->sei.alternative_transfer.preferred_transfer_characteristics;
+    }
+
     return 0;
 }