mirror of https://bitbucket.org/ausocean/av.git
81 lines
1.9 KiB
Go
81 lines
1.9 KiB
Go
/*
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DESCRIPTION
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parse.go provides H.264 NAL unit parsing utilities for the extraction of
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syntax elements.
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AUTHORS
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Saxon A. Nelson-Milton <saxon@ausocean.org>
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Dan Kortschak <dan@ausocean.org>
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LICENSE
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Copyright (C) 2017-2018 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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in gpl.txt. If not, see http://www.gnu.org/licenses.
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*/
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package h264
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import (
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"errors"
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"bitbucket.org/ausocean/av/codec/h264/h264dec"
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)
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var errNotEnoughBytes = errors.New("not enough bytes to read")
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// NALType returns the NAL type of the given NAL unit bytes. The given NAL unit
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// may be in byte stream or packet format.
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// NB: access unit delimiters are skipped.
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func NALType(n []byte) (int, error) {
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sc := frameScanner{buf: n}
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for {
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b, ok := sc.readByte()
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if !ok {
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return 0, errNotEnoughBytes
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}
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for i := 1; b == 0x00 && i != 4; i++ {
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b, ok = sc.readByte()
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if !ok {
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return 0, errNotEnoughBytes
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}
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if b != 0x01 || (i != 2 && i != 3) {
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continue
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}
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b, ok = sc.readByte()
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if !ok {
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return 0, errNotEnoughBytes
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}
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nalType := int(b & 0x1f)
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if nalType != h264dec.NALTypeAccessUnitDelimiter {
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return nalType, nil
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}
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}
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}
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}
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type frameScanner struct {
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off int
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buf []byte
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}
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func (s *frameScanner) readByte() (b byte, ok bool) {
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if s.off >= len(s.buf) {
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return 0, false
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}
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b = s.buf[s.off]
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s.off++
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return b, true
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}
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