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package mpeg
import (
"bytes"
"io"
"github.com/wader/fq/pkg/bitio"
"github.com/wader/fq/pkg/decode"
"github.com/wader/fq/pkg/interp"
)
func init() {
interp.RegisterFunc0("nal_unescape", makeBinaryTransformFn(func(r io.Reader) (io.Reader, error) {
return &nalUnescapeReader{Reader: r}, nil
}))
}
// transform to binary using fn
func makeBinaryTransformFn(fn func(r io.Reader) (io.Reader, error)) func(_ *interp.Interp, c any) any {
return func(_ *interp.Interp, c any) any {
inBR, err := interp.ToBitReader(c)
if err != nil {
return err
}
r, err := fn(bitio.NewIOReader(inBR))
if err != nil {
return err
}
outBuf := &bytes.Buffer{}
if _, err := io.Copy(outBuf, r); err != nil {
return err
}
outBR := bitio.NewBitReader(outBuf.Bytes(), -1)
bb, err := interp.NewBinaryFromBitReader(outBR, 8, 0)
if err != nil {
return err
}
return bb
}
}
func decodeEscapeValueFn(add int, b1 int, b2 int, b3 int) func(d *decode.D) uint64 {
return func(d *decode.D) uint64 {
n1 := d.U(b1)
n := n1
if n1 == (1<<b1)-1 {
n2 := d.U(b2)
if add != -1 {
n += n2 + uint64(add)
} else {
n = n2
}
if n2 == (1<<b2)-1 {
n3 := d.U(b3)
if add != -1 {
n += n3 + uint64(add)
} else {
n = n3
}
}
}
return n
}
}
// use last non-escaped value
func decodeEscapeValueAbsFn(b1 int, b2 int, b3 int) func(d *decode.D) uint64 {
return decodeEscapeValueFn(-1, b1, b2, b3)
}
// add values and escaped values
//
//nolint:deadcode,unused
func decodeEscapeValueAddFn(b1 int, b2 int, b3 int) func(d *decode.D) uint64 {
return decodeEscapeValueFn(0, b1, b2, b3)
}
// add values and escaped values+1
func decodeEscapeValueCarryFn(b1 int, b2 int, b3 int) func(d *decode.D) uint64 {
return decodeEscapeValueFn(1, b1, b2, b3)
}
// TODO: move?
// TODO: make generic replace reader? share with id3v2 unsync?
type nalUnescapeReader struct {
io.Reader
lastTwoZeros [2]bool
}
func (r nalUnescapeReader) Read(p []byte) (n int, err error) {
n, err = r.Reader.Read(p)
ni := 0
for i, b := range p[0:n] {
if r.lastTwoZeros[0] && r.lastTwoZeros[1] && b == 0x03 {
n--
r.lastTwoZeros[0] = false
r.lastTwoZeros[1] = false
continue
} else {
r.lastTwoZeros[1] = r.lastTwoZeros[0]
r.lastTwoZeros[0] = b == 0
}
p[ni] = p[i]
ni++
}
return n, err
}
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