av/codec/h264/decode/nalunit.go

package h264

import (
	"bitbucket.org/ausocean/av/codec/h264/decode/bits"
	"github.com/pkg/errors"
)

type NalUnit struct {
	NumBytes                     int
	ForbiddenZeroBit             int
	RefIdc                       int
	Type                         int
	SvcExtensionFlag             int
	Avc3dExtensionFlag           int
	SVCExtension                 *SVCExtension
	HeaderBytes                  int
	NonIdrFlag                   int
	ViewId                       int
	AnchorPicFlag                int
	InterViewFlag                int
	ReservedOneBit               int
	ViewIdx                      int
	DepthFlag                    int
	EmulationPreventionThreeByte byte
	rbsp                         []byte
}

type SVCExtension struct {
	IdrFlag              bool
	PriorityId           int
	NoInterLayerPredFlag bool
	DependencyId         int
	QualityId            int
	TemporalId           int
	UseRefBasePicFlag    bool
	DiscardableFlag      bool
	OutputFlag           bool
	ReservedThree2Bits   int
}

func NewSVCExtension(br *bits.BitReader) (*SVCExtension, error) {
	e := &SVCExtension{}
	var err error

	e.IdrFlag, err = br.ReadBool()
	if err != nil {
		return nil, errors.Wrap(err, "could not read IdrFlag")
	}

	e.PriorityId, err = br.ReadBitsInt(6)
	if err != nil {
		return nil, errors.Wrap(err, "could not read PriorityId")
	}

	e.NoInterLayerPredFlag, err = br.ReadBool()
	if err != nil {
		return nil, errors.Wrap(err, "could not read NoInterLayerPredFlag")
	}

	e.DependencyId, err = br.ReadBitsInt(3)
	if err != nil {
		return nil, errors.Wrap(err, "could not read DependencyId")
	}

	e.QualityId, err = br.ReadBitsInt(4)
	if err != nil {
		return nil, errors.Wrap(err, "could not read QualityId")
	}

	e.TemporalId, err = br.ReadBitsInt(3)
	if err != nil {
		return nil, errors.Wrap(err, "could not read TemporalId")
	}

	e.UseRefBasePicFlag, err = br.ReadBool()
	if err != nil {
		return nil, errors.Wrap(err, "could not read UseRefBasePicFlag")
	}

	e.DiscardableFlag, err = br.ReadBool()
	if err != nil {
		return nil, errors.Wrap(err, "could not read DiscardableFlag")
	}

	e.OutputFlag, err = br.ReadBool()
	if err != nil {
		return nil, errors.Wrap(err, "could not read OutputFlag")
	}

	e.ReservedThree2Bits, err = br.ReadBitsInt(2)
	if err != nil {
		return nil, errors.Wrap(err, "could not read ReservedThree2Bits")
	}

	return e, nil
}

func NalUnitHeader3davcExtension(nalUnit *NalUnit, br *bits.BitReader) error {
	return readFields(br, []field{
		{&nalUnit.ViewIdx, "ViewIdx", 8},
		{&nalUnit.DepthFlag, "DepthFlag", 1},
		{&nalUnit.NonIdrFlag, "NonIdrFlag", 1},
		{&nalUnit.TemporalId, "TemporalId", 3},
		{&nalUnit.AnchorPicFlag, "AnchorPicFlag", 1},
		{&nalUnit.InterViewFlag, "InterViewFlag", 1},
	})
}

func NalUnitHeaderMvcExtension(nalUnit *NalUnit, br *bits.BitReader) error {
	return readFields(br, []field{
		{&nalUnit.NonIdrFlag, "NonIdrFlag", 1},
		{&nalUnit.PriorityId, "PriorityId", 6},
		{&nalUnit.ViewId, "ViewId", 10},
		{&nalUnit.TemporalId, "TemporalId", 3},
		{&nalUnit.AnchorPicFlag, "AnchorPicFlag", 1},
		{&nalUnit.InterViewFlag, "InterViewFlag", 1},
		{&nalUnit.ReservedOneBit, "ReservedOneBit", 1},
	})
}

func (n *NalUnit) RBSP() []byte {
	return n.rbsp
}

func NewNalUnit(frame []byte, numBytesInNal int) (*NalUnit, error) {
	logger.Printf("debug: reading %d byte NAL\n", numBytesInNal)
	nalUnit := NalUnit{
		NumBytes:    numBytesInNal,
		HeaderBytes: 1,
	}
	// TODO: pass in actual io.Reader to NewBitReader
	br := bits.NewBitReader(nil)

	err := readFields(br, []field{
		{&nalUnit.ForbiddenZeroBit, "ForbiddenZeroBit", 1},
		{&nalUnit.RefIdc, "NalRefIdc", 2},
		{&nalUnit.Type, "NalUnitType", 5},
	})
	if err != nil {
		return nil, err
	}

	if nalUnit.Type == 14 || nalUnit.Type == 20 || nalUnit.Type == 21 {
		if nalUnit.Type != 21 {
			b, err := br.ReadBits(1)
			if err != nil {
				return nil, errors.Wrap(err, "could not read SvcExtensionFlag")
			}
			nalUnit.SvcExtensionFlag = int(b)
		} else {
			b, err := br.ReadBits(1)
			if err != nil {
				return nil, errors.Wrap(err, "could not read Avc3dExtensionFlag")
			}
			nalUnit.Avc3dExtensionFlag = int(b)
		}
		if nalUnit.SvcExtensionFlag == 1 {
			NalUnitHeaderSvcExtension(&nalUnit, br)
			nalUnit.HeaderBytes += 3
		} else if nalUnit.Avc3dExtensionFlag == 1 {
			NalUnitHeader3davcExtension(&nalUnit, br)
			nalUnit.HeaderBytes += 2
		} else {
			NalUnitHeaderMvcExtension(&nalUnit, br)
			nalUnit.HeaderBytes += 3

		}
	}

	logger.Printf("debug: found %d byte header. Reading body\n", nalUnit.HeaderBytes)
	for i := nalUnit.HeaderBytes; i < nalUnit.NumBytes; i++ {
		next3Bytes, err := br.PeekBits(24)
		if err != nil {
			logger.Printf("error: while reading next 3 NAL bytes: %v\n", err)
			break
		}
		// Little odd, the err above and the i+2 check might be synonyms
		if i+2 < nalUnit.NumBytes && next3Bytes == 0x000003 {
			for j := 0; j < 2; j++ {
				rbspByte, err := br.ReadBits(8)
				if err != nil {
					return nil, errors.Wrap(err, "could not read rbspByte")
				}
				nalUnit.rbsp = append(nalUnit.rbsp, byte(rbspByte))
			}
			i += 2

			// Read Emulation prevention three byte.
			eptByte, err := br.ReadBits(8)
			if err != nil {
				return nil, errors.Wrap(err, "could not read eptByte")
			}
			nalUnit.EmulationPreventionThreeByte = byte(eptByte)
		} else {
			if b, err := br.ReadBits(8); err == nil {
				nalUnit.rbsp = append(nalUnit.rbsp, byte(b))
			} else {
				logger.Printf("error: while reading byte %d of %d nal bytes: %v\n", i, nalUnit.NumBytes, err)
				break
			}
		}
	}

	// nalUnit.rbsp = frame[nalUnit.HeaderBytes:]
	logger.Printf("info: decoded %s NAL with %d RBSP bytes\n", NALUnitType[nalUnit.Type], len(nalUnit.rbsp))
	return &nalUnit, nil
}