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stss.go
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stss.go
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package mp4
import (
"encoding/binary"
"io"
"io/ioutil"
)
// StssBox - Sync Sample Box (stss - optional)
//
// Contained in : Sample Table box (stbl)
//
// This lists all sync samples (key frames for video tracks) in the data. If absent, all samples are sync samples.
type StssBox struct {
Version byte
Flags uint32
SampleNumber []uint32
}
// DecodeStss - box-specific decode
func DecodeStss(hdr *boxHeader, startPos uint64, r io.Reader) (Box, error) {
data, err := ioutil.ReadAll(r)
if err != nil {
return nil, err
}
versionAndFlags := binary.BigEndian.Uint32(data[0:4])
b := &StssBox{
Version: byte(versionAndFlags >> 24),
Flags: versionAndFlags & flagsMask,
SampleNumber: []uint32{},
}
ec := binary.BigEndian.Uint32(data[4:8])
for i := 0; i < int(ec); i++ {
sample := binary.BigEndian.Uint32(data[(8 + 4*i):(12 + 4*i)])
b.SampleNumber = append(b.SampleNumber, sample)
}
return b, nil
}
// Type - box-specfic type
func (b *StssBox) Type() string {
return "stss"
}
// Size - box-specfic size
func (b *StssBox) Size() uint64 {
return uint64(boxHeaderSize + 8 + len(b.SampleNumber)*4)
}
// IsSyncSample - check if sample (one-based) sampleNr is a sync sample
func (b *StssBox) IsSyncSample(sampleNr uint32) (isSync bool) {
// Based on a binary search algorithm from the Go standard library code.
// i will be the lowest index such that b.SampleNumber[i] >= sampleNr
// or len(b.SampleNumber) if not possible.
nrSamples := len(b.SampleNumber)
i, j := 0, nrSamples
for i < j {
h := (i + j) >> 1
// i ≤ h < j
if b.SampleNumber[h] < sampleNr {
i = h + 1
} else {
j = h
}
}
return i < nrSamples && b.SampleNumber[i] == sampleNr
}
// Encode - box-specific encode
func (b *StssBox) Encode(w io.Writer) error {
err := EncodeHeader(b, w)
if err != nil {
return err
}
buf := makebuf(b)
sw := NewSliceWriter(buf)
versionAndFlags := (uint32(b.Version) << 24) + b.Flags
sw.WriteUint32(versionAndFlags)
sw.WriteUint32(uint32(len(b.SampleNumber)))
for i := range b.SampleNumber {
sw.WriteUint32(b.SampleNumber[i])
}
_, err = w.Write(buf)
return err
}
func (b *StssBox) Info(w io.Writer, specificBoxLevels, indent, indentStep string) error {
bd := newInfoDumper(w, indent, b, int(b.Version), b.Flags)
level := getInfoLevel(b, specificBoxLevels)
if level >= 1 {
for i := range b.SampleNumber {
bd.write(" - syncSample[%d]: sampleNumber=%d", i+1, b.SampleNumber[i])
}
}
return bd.err
}