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// Copyright 2019, Chef. All rights reserved.
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// https://github.com/q191201771/lal
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//
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// Use of this source code is governed by a MIT-style license
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// that can be found in the License file.
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//
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// Author: Chef (191201771@qq.com)
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package aac
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import (
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"errors"
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"github.com/q191201771/naza/pkg/nazabits"
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"github.com/q191201771/naza/pkg/nazalog"
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)
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var ErrAAC = errors.New("lal.aac: fxxk")
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// Audio Data Transport Stream
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type ADTS struct {
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audioObjectType uint8
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samplingFrequencyIndex uint8
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channelConfiguration uint8
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adtsHeader []byte
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}
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type sequenceHeader struct {
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soundFormat uint8
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soundRate uint8
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soundSize uint8
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soundType uint8
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aacPacketType uint8
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}
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// 传入AAC Sequence Header，调用GetADTS时需要使用
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//
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// @param <payload> rtmp message payload，包含前面2个字节
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func (a *ADTS) PutAACSequenceHeader(payload []byte) error {
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if len(payload) < 4 {
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nazalog.Warnf("aac seq header length invalid. len=%d", len(payload))
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return ErrAAC
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}
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// <spec-video_file_format_spec_v10.pdf>, <Audio tags, AUDIODATA>, <page 10/48>
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// ----------------------------------------------------------------------------
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// soundFormat [4b] 10=AAC
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// soundRate [2b] 3=44kHz. AAC always 3
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// soundSize [1b] 0=snd8Bit, 1=snd16Bit
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// soundType [1b] 0=sndMono, 1=sndStereo. AAC always 1
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// aacPackageType [8b] 0=seq header, 1=AAC raw
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br := nazabits.NewBitReader(payload)
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var sh sequenceHeader
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sh.soundFormat, _ = br.ReadBits8(4)
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sh.soundRate, _ = br.ReadBits8(2)
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sh.soundSize, _ = br.ReadBits8(1)
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sh.soundType, _ = br.ReadBits8(1)
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sh.aacPacketType, _ = br.ReadBits8(8)
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_ = sh
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//nazalog.Debugf("%s %+v", hex.Dump(payload[:4]), sh)
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// <ISO_IEC_14496-3.pdf>
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// <1.6.2.1 AudioSpecificConfig>, <page 33/110>
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// <1.5.1.1 Audio Object type definition>, <page 23/110>
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// <1.6.3.3 samplingFrequencyIndex>, <page 35/110>
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// <1.6.3.4 channelConfiguration>
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// --------------------------------------------------------
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// audio object type [5b] 2=AAC LC
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// samplingFrequencyIndex [4b] 3=48000 4=44100
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// channelConfiguration [4b] 2=left, right front speakers
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a.audioObjectType, _ = br.ReadBits8(5)
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a.samplingFrequencyIndex, _ = br.ReadBits8(4)
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a.channelConfiguration, _ = br.ReadBits8(4)
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//nazalog.Debugf("%+v", a)
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if a.adtsHeader == nil {
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a.adtsHeader = make([]byte, 7)
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}
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return nil
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}
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// 获取ADTS头，注意，由于ADTS头依赖包的长度，而每个包的长度不同，所以生成的每个包的ADTS头也不同
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//
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// @param <length> rtmp message payload长度，包含前面2个字节
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func (a *ADTS) GetADTS(length uint16) ([]byte, error) {
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if a.IsNil() {
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return nil, ErrAAC
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}
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// <ISO_IEC_14496-3.pdf>
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// <1.A.2.2.1 Fixed Header of ADTS>, <page 75/110>
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// <1.A.2.2.2 Variable Header of ADTS>, <page 76/110>
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// <1.A.3.2.1 Definitions: Bitstream elements for ADTS>
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// ----------------------------------------------------
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// Syncword [12b] '1111 1111 1111'
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// ID [1b] 1=MPEG-2 AAC 0=MPEG-4
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// Layer [2b]
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// protection_absent [1b] 1=no crc check
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// Profile_ObjectType [2b]
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// sampling_frequency_index [4b]
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// private_bit [1b]
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// channel_configuration [3b]
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// origin/copy [1b]
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// home [1b]
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// Emphasis???
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// ------------------------------------
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// copyright_identification_bit [1b]
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// copyright_identification_start [1b]
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// aac_frame_length [13b]
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// adts_buffer_fullness [11b]
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// no_raw_data_blocks_in_frame [2b]
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// 减去头2字节，再加上自身adts头的7个字节
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length += 5
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bw := nazabits.NewBitWriter(a.adtsHeader)
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// Syncword 0(8) 1(4)
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bw.WriteBits16(12, 0xFFF)
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// ID, Layer, protection_absent 1(4)
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bw.WriteBits8(4, 0x1)
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// 2(2)
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bw.WriteBits8(2, a.audioObjectType-1)
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// 2(4)
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bw.WriteBits8(4, a.samplingFrequencyIndex)
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// private_bit 2(1)
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bw.WriteBits8(1, 0)
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// 2(1) 3(2)
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bw.WriteBits8(3, a.channelConfiguration)
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// origin/copy, home, copyright_identification_bit, copyright_identification_start 3(4)
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bw.WriteBits8(4, 0)
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// 3(2) 4(8) 5(3)
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bw.WriteBits16(13, length)
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// adts_buffer_fullness 5(5) 6(6)
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bw.WriteBits16(11, 0x7FF)
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// no_raw_data_blocks_in_frame 6(2)
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bw.WriteBits8(2, 0)
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return a.adtsHeader, nil
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}
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// 可用于判断，是否调用过ADTS.PutAACSequenceHeader
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func (a *ADTS) IsNil() bool {
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return a.adtsHeader == nil
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}
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