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annexb.go
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annexb.go
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package h264
import (
"fmt"
)
// AnnexBUnmarshal decodes NALUs from the Annex-B stream format.
func AnnexBUnmarshal(byts []byte) ([][]byte, error) {
bl := len(byts)
initZeroCount := 0
outer:
for i := 0; i < bl; i++ {
switch byts[i] {
case 0:
initZeroCount++
case 1:
break outer
default:
return nil, fmt.Errorf("unexpected byte: %d", byts[i])
}
}
if initZeroCount != 2 && initZeroCount != 3 {
return nil, fmt.Errorf("initial delimiter not found")
}
start := initZeroCount + 1
zeroCount := 0
n := 0
for i := start; i < bl; i++ {
switch byts[i] {
case 0:
zeroCount++
case 1:
if zeroCount == 2 || zeroCount == 3 {
n++
}
zeroCount = 0
default:
zeroCount = 0
}
}
if (n + 1) > MaxNALUsPerGroup {
return nil, fmt.Errorf("number of NALUs contained inside a single group (%d) is too big (maximum is %d)",
n+1, MaxNALUsPerGroup)
}
ret := make([][]byte, n+1)
pos := 0
start = initZeroCount + 1
zeroCount = 0
delimStart := 0
for i := start; i < bl; i++ {
switch byts[i] {
case 0:
if zeroCount == 0 {
delimStart = i
}
zeroCount++
case 1:
if zeroCount == 2 || zeroCount == 3 {
if (delimStart - start) > MaxNALUSize {
return nil, fmt.Errorf("NALU size (%d) is too big (maximum is %d)", delimStart-start, MaxNALUSize)
}
nalu := byts[start:delimStart]
if len(nalu) == 0 {
return nil, fmt.Errorf("empty NALU")
}
ret[pos] = nalu
pos++
start = i + 1
}
zeroCount = 0
default:
zeroCount = 0
}
}
if (bl - start) > MaxNALUSize {
return nil, fmt.Errorf("NALU size (%d) is too big (maximum is %d)", bl-start, MaxNALUSize)
}
nalu := byts[start:bl]
if len(nalu) == 0 {
return nil, fmt.Errorf("empty NALU")
}
ret[pos] = nalu
return ret, nil
}
func annexBMarshalSize(nalus [][]byte) int {
n := 0
for _, nalu := range nalus {
n += 4 + len(nalu)
}
return n
}
// AnnexBMarshal encodes NALUs into the Annex-B stream format.
func AnnexBMarshal(nalus [][]byte) ([]byte, error) {
buf := make([]byte, annexBMarshalSize(nalus))
pos := 0
for _, nalu := range nalus {
pos += copy(buf[pos:], []byte{0x00, 0x00, 0x00, 0x01})
pos += copy(buf[pos:], nalu)
}
return buf, nil
}