mirror of https://bitbucket.org/ausocean/av.git
123 lines
2.9 KiB
Go
123 lines
2.9 KiB
Go
/*
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NAME
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lex.go
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DESCRIPTION
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lex.go provides a lexer to lex h264 bytestream into access units.
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AUTHOR
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Dan Kortschak <dan@ausocean.org>
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Saxon Nelson-Milton <saxon@ausocean.org>
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LICENSE
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lex.go is Copyright (C) 2017 the Australian Ocean Lab (AusOcean)
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It is free software: you can redistribute it and/or modify them
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under the terms of the GNU General Public License as published by the
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Free Software Foundation, either version 3 of the License, or (at your
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option) any later version.
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It is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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for more details.
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You should have received a copy of the GNU General Public License
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along with revid in gpl.txt. If not, see http://www.gnu.org/licenses.
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*/
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// Package h264 provides a h264 bytestream lexer and RTP H264 access unit
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// extracter.
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package h264
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import (
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"fmt"
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"io"
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"time"
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"bitbucket.org/ausocean/av/codec/codecutil"
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)
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var noDelay = make(chan time.Time)
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func init() {
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close(noDelay)
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}
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var h264Prefix = [...]byte{0x00, 0x00, 0x01, 0x09, 0xf0}
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// Lex lexes H.264 NAL units read from src into separate writes
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// to dst with successive writes being performed not earlier than the specified
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// delay. NAL units are split after type 1 (Coded slice of a non-IDR picture), 5
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// (Coded slice of a IDR picture) and 8 (Picture parameter set).
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func Lex(dst io.Writer, src io.Reader, delay time.Duration) error {
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var tick <-chan time.Time
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if delay == 0 {
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tick = noDelay
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} else {
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ticker := time.NewTicker(delay)
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defer ticker.Stop()
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tick = ticker.C
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}
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const bufSize = 8 << 10
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c := codecutil.NewByteScanner(src, make([]byte, 4<<10)) // Standard file buffer size.
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buf := make([]byte, len(h264Prefix), bufSize)
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copy(buf, h264Prefix[:])
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writeOut := false
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for {
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var b byte
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var err error
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buf, b, err = c.ScanUntil(buf, 0x00)
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if err != nil {
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return fmt.Errorf("can't scan until: %w", err)
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}
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for n := 1; b == 0x0 && n < 4; n++ {
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b, err = c.ReadByte()
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if err != nil {
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return fmt.Errorf("can't read byte: %w", err)
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}
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buf = append(buf, b)
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if b != 0x1 || (n != 2 && n != 3) {
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continue
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}
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if writeOut {
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<-tick
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_, err := dst.Write(buf[:len(buf)-(n+1)])
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if err != nil {
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return err
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}
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buf = make([]byte, len(h264Prefix)+n, bufSize)
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copy(buf, h264Prefix[:])
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buf = append(buf, 1)
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writeOut = false
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}
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b, err = c.ReadByte()
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if err != nil {
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return fmt.Errorf("can't read byte: %w", err)
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}
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buf = append(buf, b)
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// http://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-H.264-200305-S!!PDF-E&type=items
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// Table 7-1 NAL unit type codes
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const (
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nonIdrPic = 1
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idrPic = 5
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suppEnhInfo = 6
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paramSet = 8
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)
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switch nalTyp := b & 0x1f; nalTyp {
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case nonIdrPic, idrPic, paramSet, suppEnhInfo:
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writeOut = true
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}
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}
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}
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}
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