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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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soundFormat := nazabits.GetBits8(payload[0], 4, 4)
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soundRate := nazabits.GetBits8(payload[0], 2, 2)
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soundSize := nazabits.GetBit8(payload[0], 1)
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soundType := nazabits.GetBit8(payload[0], 0)
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aacPacketType := payload[1]
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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 = uint8(nazabits.GetBits16(payload[2:], 11, 5))
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obj.samplingFrequencyIndex = uint8(nazabits.GetBits16(payload[2:], 7, 4))
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obj.channelConfiguration = uint8(nazabits.GetBits16(payload[2:], 3, 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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obj.adtsHeader[0] = 0xff
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obj.adtsHeader[1] = 0xf1
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obj.adtsHeader[2] = ((obj.audioObjectType - 1) << 6) & 0xc0
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obj.adtsHeader[2] |= (obj.samplingFrequencyIndex << 2) & 0x3c
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obj.adtsHeader[2] |= (obj.channelConfiguration >> 2) & 0x01
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obj.adtsHeader[3] = (obj.channelConfiguration << 6) & 0xc0
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// 减去前面2个字节，再加上加上adts的7个字节
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length += 5
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obj.adtsHeader[3] += uint8(length >> 11) // TODO chef: 为什么这样做，应该只是使用2个字节，取5个再相加是否会超出？
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obj.adtsHeader[4] = uint8((length & 0x7ff) >> 3)
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obj.adtsHeader[5] = uint8((length & 0x07) << 5)
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obj.adtsHeader[5] |= 0x1f
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obj.adtsHeader[6] = 0xfc
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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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