/* NAME parse.go DESCRIPTION See Readme.md AUTHOR Dan Kortschak <dan@ausocean.org> LICENSE parse.go is Copyright (C) 2017 the Australian Ocean Lab (AusOcean) It is free software: you can redistribute it and/or modify them under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. It is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with revid in gpl.txt. If not, see http://www.gnu.org/licenses. */ // Package parse provides parsers for video encodings. package parse import ( "bufio" "bytes" "fmt" "io" "time" ) var noDelay = make(chan time.Time) func init() { close(noDelay) } var h264Prefix = [...]byte{0x00, 0x00, 0x01, 0x09, 0xf0} // H264 lexes H.264 NAL units read from src into separate writes to dst with // successive writes being performed not earlier than the specified delay. // NAL units are split after type 1 (Coded slice of a non-IDR picture), 5 // (Coded slice of a IDR picture) and 8 (Picture parameter set). func H264(dst io.Writer, src io.Reader, delay time.Duration) error { var tick <-chan time.Time if delay == 0 { tick = noDelay } else { ticker := time.NewTicker(delay) defer ticker.Stop() tick = ticker.C } const bufSize = 8 << 10 c := newScanner(src, make([]byte, 4<<10)) // Standard file buffer size. buf := make([]byte, len(h264Prefix), bufSize) copy(buf, h264Prefix[:]) writeOut := false outer: for { var b byte var err error buf, b, err = c.scanUntilZeroInto(buf) if err != nil { if err != io.EOF { return err } break } for n := 1; b == 0x0 && n < 4; n++ { b, err = c.readByte() if err != nil { if err != io.EOF { return err } break outer } buf = append(buf, b) if b != 0x1 || (n != 2 && n != 3) { continue } if writeOut { <-tick _, err := dst.Write(buf[:len(buf)-(n+1)]) if err != nil { return err } buf = make([]byte, len(h264Prefix)+n, bufSize) copy(buf, h264Prefix[:]) buf = append(buf, 1) writeOut = false } b, err = c.readByte() if err != nil { if err != io.EOF { return err } break outer } buf = append(buf, b) // http://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-H.264-200305-S!!PDF-E&type=items // Table 7-1 NAL unit type codes const ( nonIdrPic = 1 idrPic = 5 paramSet = 8 ) switch nalTyp := b & 0x1f; nalTyp { case nonIdrPic, idrPic, paramSet: writeOut = true } } } if len(buf) == len(h264Prefix) { return nil } <-tick _, err := dst.Write(buf) return err } // scanner is a byte scanner. type scanner struct { buf []byte off int // r is the source of data for the scanner. r io.Reader } // newScanner returns a scanner initialised with an io.Reader and a read buffer. func newScanner(r io.Reader, buf []byte) *scanner { return &scanner{r: r, buf: buf[:0]} } // scanUntilZeroInto scans the scanner's underlying io.Reader until a zero byte // has been read, appending all read bytes to dst. The resulting appended data, // the last read byte and whether the last read byte was zero are returned. func (c *scanner) scanUntilZeroInto(dst []byte) (res []byte, b byte, err error) { outer: for { var i int for i, b = range c.buf[c.off:] { if b != 0x0 { continue } dst = append(dst, c.buf[c.off:c.off+i+1]...) c.off += i + 1 break outer } dst = append(dst, c.buf[c.off:]...) err = c.reload() if err != nil { break } } return dst, b, err } // readByte is an unexported ReadByte. func (c *scanner) readByte() (byte, error) { if c.off >= len(c.buf) { err := c.reload() if err != nil { return 0, err } } b := c.buf[c.off] c.off++ return b, nil } // reload re-fills the scanner's buffer. func (c *scanner) reload() error { n, err := c.r.Read(c.buf[:cap(c.buf)]) c.buf = c.buf[:n] if err != nil { if err != io.EOF { return err } if n == 0 { return io.EOF } } c.off = 0 return nil } // MJPEG parses MJPEG frames read from src into separate writes to dst with // successive writes being performed not earlier than the specified delay. func MJPEG(dst io.Writer, src io.Reader, delay time.Duration) error { var tick <-chan time.Time if delay == 0 { tick = noDelay } else { ticker := time.NewTicker(delay) defer ticker.Stop() tick = ticker.C } r := bufio.NewReader(src) for { buf := make([]byte, 2, 4<<10) n, err := r.Read(buf) if n < 2 { return nil } if err != nil { return err } if !bytes.Equal(buf, []byte{0xff, 0xd8}) { return fmt.Errorf("parser: not MJPEG frame start: %#v", buf) } var last byte for { b, err := r.ReadByte() if err != nil { return err } buf = append(buf, b) if last == 0xff && b == 0xd9 { break } last = b } <-tick _, err = dst.Write(buf) if err != nil { return err } } }