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, 8 insertions, 1 deletions

diff --git a/libavcodec/h264_sei.h b/libavcodec/h264_sei.h
index da3b391860..5f5d895e89 100644
--- a/libavcodec/h264_sei.h
+++ b/libavcodec/h264_sei.h
@@ -32,7 +32,8 @@ typedef enum {
     SEI_TYPE_RECOVERY_POINT         = 6,   ///< recovery point (frame # to decoder sync)
     SEI_TYPE_FRAME_PACKING          = 45,  ///< frame packing arrangement
     SEI_TYPE_DISPLAY_ORIENTATION    = 47,  ///< display orientation
-    SEI_TYPE_GREEN_METADATA         = 56   ///< GreenMPEG information
+    SEI_TYPE_GREEN_METADATA         = 56,  ///< GreenMPEG information
+    SEI_TYPE_ALTERNATIVE_TRANSFER   = 147, ///< alternative transfer
 } SEI_Type;
 
 /**
@@ -144,6 +145,11 @@ typedef struct H264SEIGreenMetaData {
     uint16_t xsd_metric_value;
 } H264SEIGreenMetaData;
 
+typedef struct H264SEIAlternativeTransfer {
+    int present;
+    int preferred_transfer_characteristics;
+} H264SEIAlternativeTransfer;
+
 typedef struct H264SEIContext {
     H264SEIPictureTiming picture_timing;
     H264SEIAFD afd;
@@ -154,6 +160,7 @@ typedef struct H264SEIContext {
     H264SEIFramePacking frame_packing;
     H264SEIDisplayOrientation display_orientation;
     H264SEIGreenMetaData green_metadata;
+    H264SEIAlternativeTransfer alternative_transfer;
 } H264SEIContext;
 
 struct H264ParamSets;