[AAC]ADTS解析及ASC生成

void Adts2Asc(uint8_t* pData, int nSize) {
       // 判断是否为adts格式的aac数据，如果不是则返回失败
		if (nSize < 7 || pData[0] != 0xFF || (pData[1] & 0xF0) != 0xF0) {
			JmixcLogError("Invalid aac frame, only support adts format");
			return nSize;
		}
		
		int adtsHeaderLen = 7;
		if (0 == pData[1] & 0x01) {
			adtsHeaderLen = 9; // 包含2字节的crc校验码
		}
		// 1、adts解析
		/*pData[0] << 8 | pData[1] & 0xF0;                               // 0xFFF0   同步字段                              总是0xFFF,代表一个ADTS帧的开始，作为分界符，用于同步每帧起始位置
		(pData[1] & 0x08) >> 3;                                        // 0/1      ID                                   0 for MPEG-4, 1 for MPEG-2
		(pData[1] & 0x06) >> 1;                                        // 0/1/2    Layer                                总是0
		pData[1] & 0x01;                                               // 0/1      Protection absent                     set to 1 if there is no CRC and 0 if there is CRC
		(pData[2] & 0xC0) >> 6;                                        // 0~3      Profile                               0 Main, 1 LC, 2 SSR, 3 LTP,profile的值等于 Audio Object Type的值减1
		(pData[2] & 0x3C) >> 2;                                        // 0~15     Sampling Frequency Index MPEG-4       Sampling Frequency Index (15 is forbidden)
		(pData[2] & 0x02) >> 1;                                        // 0/1      Private bit                           总是0
		(pData[2] & 0x01) << 2 | (pData[3] & 0xC0) >> 6;               // 0/1      Channel Configuration MPEG-4          Channel Configuration (in case of AAC Main: 0 = 1 Channel: Front-center channel)
		(pData[3] & 0x20) >> 5;                                        // 0/1      Originality                           总是0
		(pData[3] & 0x10) >> 4;                                        // 0/1      Home                                  总是0
		(pData[3] & 0x08) >> 3;                                        // 0/1      Copyright identification bit          总是0
		(pData[3] & 0x04) >> 2;                                        // 0/1      Copyright identification start        总是0
		(pData[3] & 0x03) << 11 | pData[4] << 3 |(pData[5] & 0xE0) >> 5; //        Frame length                          一个 ADTS 帧的长度包括 ADTS 头和 AAC 原始流.this value must include 7 or 9 bytes of header length FrameLength = (ProtectionAbsent == 1 ? 7 : 9) + size(AACFrame)
		(pData[5] & 0x1F) << 6 | (pData[6] & 0xFC) >> 2;                 //        Buffer fullness                       0x7FF indicates that this frame uses the full available bit rate.
		pData[6] & 0x03;                                                 //        Number of raw data blocks in frame    1 to 4,ADTS 帧中有 number_of_raw_data_blocks_in_frame + 1 个 AAC 原始帧
		*/
		// asc
		int profile = ((pData[2] & 0xC0) >> 6) + 1;
		int sampleFrequencyIndex = (pData[2] & 0x3C) >> 2;
		int channelConfig = ((pData[2] & 0x01) << 2) | ((pData[3] & 0xC0) >> 6);
		uint8_t asc[2] = {0};
		asc[0] = (profile << 3) | ((sampleFrequencyIndex >> 1) & 0x07);
		asc[1] = ((sampleFrequencyIndex & 0x01) << 7) | ((channelConfig & 0x0F) << 3) | (0 << 2) | (0 << 1) | 0;
}