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package aac
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import (
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"encoding/hex"
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"github.com/q191201771/lal/pkg/util/log"
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"io"
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)
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var adts ADTS
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type ADTS struct {
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audioObjectType uint8
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samplingFrequencyIndex uint8
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channelConfig uint8
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frameLengthFlag uint8
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dependOnCoreCoder uint8
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extensionFlag uint8
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adtsHeader []byte
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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 (obj *ADTS) PutAACSequenceHeader(payload []byte) {
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soundFormat := payload[0] >> 4 // 10=AAC
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soundRate := (payload[0] >> 2) & 0x03 // 3=44kHz. For AAC: always 3
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soundSize := (payload[0] >> 1) & 0x01 // 0=snd8Bit 1=snd16Bit
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soundType := payload[0] & 0x01 // For AAC: always 1
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//aacPacketType := payload[1] // 0:sequence header 1:AAC raw
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obj.audioObjectType = (payload[2] & 0xf8) >> 3 // 5bit 编码结构类型
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obj.samplingFrequencyIndex = ((payload[2] & 0x07) << 1) | (payload[3] >> 7) // 4bit 音频采样率索引值
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obj.channelConfig = (payload[3] & 0x78) >> 3 // 4bit 音频输出声道
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obj.frameLengthFlag = (payload[3] & 0x04) >> 2 // 1bit
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obj.dependOnCoreCoder = (payload[3] & 0x02) >> 1 // 1bit
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obj.extensionFlag = payload[3] & 0x01 // 1bit
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log.Debugf(hex.Dump(payload[:4]))
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log.Debugf("%d %d %d %d", soundFormat, soundRate, soundSize, soundType)
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log.Debugf("%+v", obj)
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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 (obj *ADTS) GetADTS(length uint16) []byte {
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// adts fixed header:
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// syncword 12bit (0: **** ****, 1: **** 0000) 0xfff
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// ID 1bit (1: 0000 *000) 0 0:MPEG-4 1:MPEG-2
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// layer 2bit (1: 0000 0**0) 0
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// protection_absent 1bit (1: 0000 000*) 1
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// profile 2bit (2: **00 0000)
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// sampling_frequency_index 4bit (2: 00** **00)
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// private_bit 1bit (2: 0000 00*0) 0
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// channel_configuration 3bit (2: 0000 000*, 3: **00 0000)
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// origin_copy 1bit (3: 00*0 0000) 0
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// home 1bit (3: 000* 0000) 0
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//
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// adts variable_header:
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// copyright_identification_bit 1bit (3: 0000 *000) 0
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// copyright_identification_start 1bit (3: 0000 0*00) 0
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// aac_frame_length 13bit (3: 0000 00**, 5: ***0 0000)
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// adts_buffer_fullness 11bit (5: 000* ****, 6: **** **00) 0x7ff
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// number_of_raw_data_blocks_in_frame 2bit (6: 0000 00**) 0
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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.channelConfig >> 2) & 0x01
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obj.adtsHeader[3] = (obj.channelConfig << 6) & 0xc0
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// 减去前面2个字节，加上adts的7个字节
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length = length - 2 + 7
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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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// @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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