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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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"encoding/hex"
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"io"
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"github.com/q191201771/naza/pkg/nazabits"
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log "github.com/q191201771/naza/pkg/nazalog"
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)
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// TODO chef: 把Seq Header头两字节的解析和ADTS的内容分离开
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var adts ADTS
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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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// 传入AAC Sequence Header，调用GetADTS时需要使用
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// @param <payload> rtmp message payload，包含前面2个字节
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func (obj *ADTS) PutAACSequenceHeader(payload []byte) {
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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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soundFormat := br.ReadBits8(4)
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soundRate := br.ReadBits8(2)
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soundSize := br.ReadBits8(1)
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soundType := br.ReadBits8(1)
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aacPacketType := br.ReadBits8(8)
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log.Debugf("%s %d %d %d %d %d", hex.Dump(payload[:4]), soundFormat, soundRate, soundSize, soundType, aacPacketType)
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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
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// channelConfiguration [4b] 2=left, right front speakers
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obj.audioObjectType = br.ReadBits8(5)
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obj.samplingFrequencyIndex = br.ReadBits8(4)
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obj.channelConfiguration = br.ReadBits8(4)
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log.Debugf("%+v", obj)
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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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// @param <length> rtmp message payload长度，包含前面2个字节
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func (obj *ADTS) GetADTS(length uint16) []byte {
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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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if obj.adtsHeader == nil {
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obj.adtsHeader = make([]byte, 7)
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}
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// 减去头两字节，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(obj.adtsHeader)
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bw.WriteBits16(12, 0xFFF) // Syncword 0(8) 1(4)
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bw.WriteBits8(4, 0x1) // ID, Layer, protection_absent 1(4)
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bw.WriteBits8(2, obj.audioObjectType-1) // 2(2)
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bw.WriteBits8(4, obj.samplingFrequencyIndex) // 2(4)
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bw.WriteBits8(1, 0) // private_bit 2(1)
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bw.WriteBits8(3, obj.channelConfiguration) // 2(1) 3(2)
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bw.WriteBits8(4, 0) // origin/copy, home, copyright_identification_bit, copyright_identification_start 3(4)
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bw.WriteBits16(13, length) // 3(2) 4(8) 5(3)
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bw.WriteBits16(11, 0x7FF) // adts_buffer_fullness 5(5) 6(6)
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bw.WriteBits8(2, 0) // no_raw_data_blocks_in_frame 6(2)
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return obj.adtsHeader
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}
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// 将 rtmp AAC 传入，输出带 ADTS 头的 AAC ES流
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// @param <payload> rtmp message payload部分
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func CaptureAAC(w io.Writer, payload []byte) {
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if payload[1] == 0 {
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adts.PutAACSequenceHeader(payload)
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return
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}
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_, _ = w.Write(adts.GetADTS(uint16(len(payload))))
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_, _ = w.Write(payload[2:])
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}
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