/* NAME lex.go DESCRIPTION lex.go provides a lexer to lex h264 bytestream into access units. AUTHOR Dan Kortschak <dan@ausocean.org> Saxon Nelson-Milton <saxon@ausocean.org> LICENSE lex.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 h264 provides a h264 bytestream lexer and RTP H264 access unit // extracter. package h264 import ( "io" "time" "bitbucket.org/ausocean/av/codec/codecutil" ) var noDelay = make(chan time.Time) func init() { close(noDelay) } var h264Prefix = [...]byte{0x00, 0x00, 0x01, 0x09, 0xf0} // Lex 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 Lex(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 := codecutil.NewByteScanner(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.ScanUntil(buf, 0x00) 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 suppEnhInfo = 6 paramSet = 8 ) switch nalTyp := b & 0x1f; nalTyp { case nonIdrPic, idrPic, paramSet, suppEnhInfo: writeOut = true } } } if len(buf) == len(h264Prefix) { return nil } <-tick _, err := dst.Write(buf) return err }