codec/h264/h264dec: commenting for NAL uni syntax structure fields

codec/h264/h264dec/nalunit.go

@@ -19,13 +19,29 @@ import (
 
 // MVCExtension describes a NAL unit header multiview video coding extension, as
 // defined in section H.7.3.1.1 of the specifications.
+// Semantics of fields are specified in section H.7.4.1.1.
 type MVCExtension struct {
-	NonIdrFlag     bool
-	PriorityID     int
-	ViewID         int
-	TemporalID     int
-	AnchorPicFlag  bool
-	InterViewFlag  bool
+	// non_idr_flag, if true indicates that access unit is not IDR.
+	NonIdrFlag bool
+
+	// priority_id, indicates priority of NAL unit. A lower value => higher priority.
+	PriorityID int
+
+	// view_id, specifies a view identifier for the unit. Units with identical
+	// view_id are in the same view.
+	ViewID int
+
+	// temporal_id, temporal identifier for the unit.
+	TemporalID int
+
+	// anchor_pic_flag, if true access unit is an anchor access unit.
+	AnchorPicFlag bool
+
+	// inter_view_flag, if false current view component not used for inter-view
+	// prediction elsewhere in access unit.
+	InterViewFlag bool
+
+	// reserved_one_bit, always 1 (ignored by decoders)
 	ReservedOneBit int
 }
 
@@ -76,12 +92,26 @@ func NewMVCExtension(br *bits.BitReader) (*MVCExtension, error) {
 
 // ThreeDAVCExtension describes a NAL unit header 3D advanced video coding
 // extension, as defined in section J.7.3.1.1 of the specifications.
+// For field semantics see section J.7.4.1.1.
 type ThreeDAVCExtension struct {
-	ViewIdx       int
-	DepthFlag     bool
-	NonIdrFlag    bool
-	TemporalID    int
+	// view_idx, specifies the order index for the NAL i.e. view_id = view_id[view_idx].
+	ViewIdx int
+
+	// dpeth_flag, if true indicates NAL part of a depth view component, otherwise
+	// a texture view component.
+	DepthFlag bool
+
+	// non_idr_flag, if true indicates that access unit is not IDR.
+	NonIdrFlag bool
+
+	// temporal_id, temporal identifier for the unit.
+	TemporalID int
+
+	// anchor_pic_flag, if true access unit is an anchor access unit.
 	AnchorPicFlag bool
+
+	// inter_view_flag, if false current view component not used for inter-view
+	// prediction elsewhere in access unit.
 	InterViewFlag bool
 }
 
@@ -127,17 +157,44 @@ func NewThreeDAVCExtension(br *bits.BitReader) (*ThreeDAVCExtension, error) {
 
 // SVCExtension describes a NAL unit header scalable video coding extension, as
 // defined in section G.7.3.1.1 of the specifications.
+// For field semantics see section G.7.4.1.1.
 type SVCExtension struct {
-	IdrFlag              bool
-	PriorityID           int
+	// idr_flag, if true the current coded picture is an IDR picture when
+	// dependency_id == max(dependency_id) in the coded picture.
+	IdrFlag bool
+
+	// priority_id, specifies priority identifier for unit.
+	PriorityID int
+
+	// no_inter_layer_pred_flag, if true inter-layer prediction can't be used for
+	// decoding slice.
 	NoInterLayerPredFlag bool
-	DependencyID         int
-	QualityID            int
-	TemporalID           int
-	UseRefBasePicFlag    bool
-	DiscardableFlag      bool
-	OutputFlag           bool
-	ReservedThree2Bits   int
+
+	// dependency_id, specifies a dependency identifier for the NAL.
+	DependencyID int
+
+	// quality_id, specifies a quality identifier for the NAL.
+	QualityID int
+
+	// temporal_id, specifiesa temporal identifier for the NAL.
+	TemporalID int
+
+	// use_ref_base_pic_flag, if true indicates reference base pictures and
+	// decoded pictures are used as references for inter prediction.
+	UseRefBasePicFlag bool
+
+	// discardable_flag, if true, indicates current NAL is not used for decoding
+	// dependency representations that are part of the current coded picture or
+	// any subsequent coded picture in decoding order and have a greater
+	// dependency_id value than current NAL.
+	DiscardableFlag bool
+
+	// output_flag, affects the decoded picture output and removal processes as
+	// specified in Annex C.
+	OutputFlag bool
+
+	// reserved_three_2bits, equal to 3. Decoders ignore.
+	ReservedThree2Bits int
 }
 
 // NewSVCExtension parses a NAL unit header scalable video coding extension from
@@ -202,17 +259,47 @@ func NewSVCExtension(br *bits.BitReader) (*SVCExtension, error) {
 
 // NALUnit describes a network abstraction layer unit, as defined in section
 // 7.3.1 of the specifications.
+// Field semantics are defined in section 7.4.1.
 type NALUnit struct {
-	ForbiddenZeroBit             int
-	RefIdc                       int
-	Type                         int
-	SVCExtensionFlag             bool
-	AVC3DExtensionFlag           bool
-	SVCExtension                 *SVCExtension
-	ThreeDAVCExtension           *ThreeDAVCExtension
-	MVCExtension                 *MVCExtension
+	// forbidden_zero_bit, always 0.
+	ForbiddenZeroBit int
+
+	// nal_ref_idc, if not 0 indicates content of NAL contains a sequence parameter
+	// set, a sequence parameter set extension, a subset sequence parameter set,
+	// a picture parameter set, a slice of a reference picture, a slice data
+	// partition of a reference picture, or a prefix NAL preceding a slice of
+	// a reference picture.
+	RefIdc int
+
+	// nal_unit_type, specifies the type of RBSP data contained in the NAL as
+	// defined in Table 7-1.
+	Type int
+
+	// svc_extension_flag, indicates whether a nal_unit_header_svc_extension()
+	// (G.7.3.1.1) or nal_unit_header_mvc_extension() (H.7.3.1.1) will follow next
+	// in the syntax structure.
+	SVCExtensionFlag bool
+
+	// avc_3d_extension_flag, for nal_unit_type = 21, indicates that a
+	// nal_unit_header_mvc_extension() (H.7.3.1.1) or
+	// nal_unit_header_3davc_extension() (J.7.3.1.1) will follow next in syntax
+	// structure.
+	AVC3DExtensionFlag bool
+
+	// nal_unit_header_svc_extension() as defined in section G.7.3.1.1.
+	SVCExtension *SVCExtension
+
+	// nal_unit_header_3davc_extension() as defined in section J.7.3.1.1
+	ThreeDAVCExtension *ThreeDAVCExtension
+
+	// nal_unit_header_mvc_extension() as defined in section H.7.3.1.1).
+	MVCExtension *MVCExtension
+
+	// emulation_prevention_three_byte, equal to 0x03 and is discarded by decoder.
 	EmulationPreventionThreeByte byte
-	RBSP                         []byte
+
+	// rbsp_byte, the raw byte sequence payload data for the NAL.
+	RBSP []byte
 }
 
 // NewNALUnit parses a network abstraction layer unit from br following the