diff --git a/codec/h264/h264dec/nalunit.go b/codec/h264/h264dec/nalunit.go
index 2e076567..2e754f12 100644
--- a/codec/h264/h264dec/nalunit.go
+++ b/codec/h264/h264dec/nalunit.go
@@ -10,6 +10,7 @@ AUTHORS
 package h264dec
 
 import (
+	"fmt"
 	"io"
 
 	"github.com/pkg/errors"
@@ -262,18 +263,18 @@ func NewSVCExtension(br *bits.BitReader) (*SVCExtension, error) {
 // Field semantics are defined in section 7.4.1.
 type NALUnit struct {
 	// forbidden_zero_bit, always 0.
-	ForbiddenZeroBit int
+	ForbiddenZeroBit uint8
 
 	// 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
+	RefIdc uint8
 
 	// nal_unit_type, specifies the type of RBSP data contained in the NAL as
 	// defined in Table 7-1.
-	Type int
+	Type uint8
 
 	// 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
@@ -306,28 +307,19 @@ type NALUnit struct {
 // syntax structure specified in section 7.3.1, and returns as a new NALUnit.
 func NewNALUnit(br *bits.BitReader) (*NALUnit, error) {
 	n := &NALUnit{}
+	r := newFieldReader(br)
 
-	err := readFields(br, []field{
-		{&n.ForbiddenZeroBit, "ForbiddenZeroBit", 1},
-		{&n.RefIdc, "NalRefIdc", 2},
-		{&n.Type, "NalUnitType", 5},
-	})
-	if err != nil {
-		return nil, err
-	}
+	n.ForbiddenZeroBit = uint8(r.readBits(1))
+	n.RefIdc = uint8(r.readBits(2))
+	n.Type = uint8(r.readBits(5))
 
 	// TODO: use consts for the NAL types here
+	var err error
 	if n.Type == 14 || n.Type == 20 || n.Type == 21 {
 		if n.Type != 21 {
-			n.SVCExtensionFlag, err = br.ReadBool()
-			if err != nil {
-				return nil, errors.Wrap(err, "could not read SVCExtensionFlag")
-			}
+			n.SVCExtensionFlag = r.readBits(1) == 1
 		} else {
-			n.AVC3DExtensionFlag, err = br.ReadBool()
-			if err != nil {
-				return nil, errors.Wrap(err, "could not read AVC3DExtensionFlag")
-			}
+			n.AVC3DExtensionFlag = r.readBits(1) == 1
 		}
 		if n.SVCExtensionFlag {
 			n.SVCExtension, err = NewSVCExtension(br)
@@ -360,27 +352,20 @@ func NewNALUnit(br *bits.BitReader) (*NALUnit, error) {
 
 		if 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")
-				}
+				rbspByte := byte(r.readBits(8))
 				n.RBSP = append(n.RBSP, byte(rbspByte))
 			}
 
 			// Read Emulation prevention three byte.
-			eptByte, err := br.ReadBits(8)
-			if err != nil {
-				return nil, errors.Wrap(err, "could not read eptByte")
-			}
-			n.EmulationPreventionThreeByte = byte(eptByte)
+			n.EmulationPreventionThreeByte = byte(r.readBits(8))
 		} else {
-			b, err := br.ReadBits(8)
-			if err != nil {
-				return nil, errors.Wrap(err, "could not read RBSP byte")
-			}
-			n.RBSP = append(n.RBSP, byte(b))
+			n.RBSP = append(n.RBSP, byte(r.readBits(8)))
 		}
 	}
 
+	if r.err() != nil {
+		return nil, fmt.Errorf("fieldReader error: %v", r.err())
+	}
+
 	return n, nil
 }
diff --git a/codec/h264/h264dec/slice.go b/codec/h264/h264dec/slice.go
index 360282a6..77e369d9 100644
--- a/codec/h264/h264dec/slice.go
+++ b/codec/h264/h264dec/slice.go
@@ -949,7 +949,7 @@ func NewSliceContext(videoStream *VideoStream, nalUnit *NALUnit, rbsp []byte, sh
 	var err error
 	sps := videoStream.SPS
 	pps := videoStream.PPS
-	logger.Printf("debug: %s RBSP %d bytes %d bits == \n", NALUnitType[nalUnit.Type], len(rbsp), len(rbsp)*8)
+	logger.Printf("debug: %s RBSP %d bytes %d bits == \n", NALUnitType[int(nalUnit.Type)], len(rbsp), len(rbsp)*8)
 	logger.Printf("debug: \t%#v\n", rbsp[0:8])
 	var idrPic bool
 	if nalUnit.Type == 5 {
@@ -974,7 +974,7 @@ func NewSliceContext(videoStream *VideoStream, nalUnit *NALUnit, rbsp []byte, sh
 	}
 
 	sliceType := sliceTypeMap[header.SliceType]
-	logger.Printf("debug: %s (%s) slice of %d bytes\n", NALUnitType[nalUnit.Type], sliceType, len(rbsp))
+	logger.Printf("debug: %s (%s) slice of %d bytes\n", NALUnitType[int(nalUnit.Type)], sliceType, len(rbsp))
 	header.PPSID, err = readUe(br)
 	if err != nil {
 		return nil, errors.Wrap(err, "could not parse PPSID")