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// Package h264reader implements a H264 Annex-B Reader
package h264reader
import (
"bytes"
"errors"
"io"
)
// H264Reader reads data from stream and constructs h264 nal units
type H264Reader struct {
stream io.Reader
nalBuffer []byte
countOfConsecutiveZeroBytes int
nalPrefixParsed bool
readBuffer []byte
tmpReadBuf []byte
}
var (
errNilReader = errors.New("stream is nil")
errDataIsNotH264Stream = errors.New("data is not a H264 bitstream")
)
// NewReader creates new H264Reader
func NewReader(in io.Reader) (*H264Reader, error) {
if in == nil {
return nil, errNilReader
}
reader := &H264Reader{
stream: in,
nalBuffer: make([]byte, 0),
nalPrefixParsed: false,
readBuffer: make([]byte, 0),
tmpReadBuf: make([]byte, 4096),
}
return reader, nil
}
// NAL H.264 Network Abstraction Layer
type NAL struct {
PictureOrderCount uint32
// NAL header
ForbiddenZeroBit bool
RefIdc uint8
UnitType NalUnitType
Data []byte // header byte + rbsp
}
func (reader *H264Reader) read(numToRead int) (data []byte, e error) {
for len(reader.readBuffer) < numToRead {
n, err := reader.stream.Read(reader.tmpReadBuf)
if err != nil {
return nil, err
}
if n == 0 {
break
}
reader.readBuffer = append(reader.readBuffer, reader.tmpReadBuf[0:n]...)
}
var numShouldRead int
if numToRead <= len(reader.readBuffer) {
numShouldRead = numToRead
} else {
numShouldRead = len(reader.readBuffer)
}
data = reader.readBuffer[0:numShouldRead]
reader.readBuffer = reader.readBuffer[numShouldRead:]
return data, nil
}
func (reader *H264Reader) bitStreamStartsWithH264Prefix() (prefixLength int, e error) {
nalPrefix3Bytes := []byte{0, 0, 1}
nalPrefix4Bytes := []byte{0, 0, 0, 1}
prefixBuffer, e := reader.read(4)
if e != nil {
return
}
n := len(prefixBuffer)
if n == 0 {
return 0, io.EOF
}
if n < 3 {
return 0, errDataIsNotH264Stream
}
nalPrefix3BytesFound := bytes.Equal(nalPrefix3Bytes, prefixBuffer[:3])
if n == 3 {
if nalPrefix3BytesFound {
return 0, io.EOF
}
return 0, errDataIsNotH264Stream
}
// n == 4
if nalPrefix3BytesFound {
reader.nalBuffer = append(reader.nalBuffer, prefixBuffer[3])
return 3, nil
}
nalPrefix4BytesFound := bytes.Equal(nalPrefix4Bytes, prefixBuffer)
if nalPrefix4BytesFound {
return 4, nil
}
return 0, errDataIsNotH264Stream
}
// NextNAL reads from stream and returns then next NAL,
// and an error if there is incomplete frame data.
// Returns all nil values when no more NALs are available.
func (reader *H264Reader) NextNAL() (*NAL, error) {
if !reader.nalPrefixParsed {
_, err := reader.bitStreamStartsWithH264Prefix()
if err != nil {
return nil, err
}
reader.nalPrefixParsed = true
}
for {
buffer, err := reader.read(1)
if err != nil {
break
}
n := len(buffer)
if n != 1 {
break
}
readByte := buffer[0]
nalFound := reader.processByte(readByte)
if nalFound {
nal := newNal(reader.nalBuffer)
nal.parseHeader()
if nal.UnitType == NalUnitTypeSEI {
reader.nalBuffer = nil
continue
}
break
}
reader.nalBuffer = append(reader.nalBuffer, readByte)
}
if len(reader.nalBuffer) == 0 {
return nil, io.EOF
}
nal := newNal(reader.nalBuffer)
reader.nalBuffer = nil
nal.parseHeader()
return nal, nil
}
func (reader *H264Reader) processByte(readByte byte) (nalFound bool) {
nalFound = false
switch readByte {
case 0:
reader.countOfConsecutiveZeroBytes++
case 1:
if reader.countOfConsecutiveZeroBytes >= 2 {
countOfConsecutiveZeroBytesInPrefix := 2
if reader.countOfConsecutiveZeroBytes > 2 {
countOfConsecutiveZeroBytesInPrefix = 3
}
if nalUnitLength := len(reader.nalBuffer) - countOfConsecutiveZeroBytesInPrefix; nalUnitLength > 0 {
reader.nalBuffer = reader.nalBuffer[0:nalUnitLength]
nalFound = true
}
}
reader.countOfConsecutiveZeroBytes = 0
default:
reader.countOfConsecutiveZeroBytes = 0
}
return nalFound
}
func newNal(data []byte) *NAL {
return &NAL{PictureOrderCount: 0, ForbiddenZeroBit: false, RefIdc: 0, UnitType: NalUnitTypeUnspecified, Data: data}
}
func (h *NAL) parseHeader() {
firstByte := h.Data[0]
h.ForbiddenZeroBit = (((firstByte & 0x80) >> 7) == 1) // 0x80 = 0b10000000
h.RefIdc = (firstByte & 0x60) >> 5 // 0x60 = 0b01100000
h.UnitType = NalUnitType((firstByte & 0x1F) >> 0) // 0x1F = 0b00011111
}
|
