ADTS格式的AAC文件解析

namespace adts
{
//采样率枚举
typedef enum
{
    ADTS_SF_96000=0,
    ADTS_SF_88200,
    ADTS_SF_64000,
    ADTS_SF_48000,
    ADTS_SF_44100,
    ADTS_SF_32000,
    ADTS_SF_24000,
    ADTS_SF_22050,
    ADTS_SF_16000,
    ADTS_SF_12000,
    ADTS_SF_11025,
    ADTS_SF_8000,
    ADTS_SF_7350,
    ADTS_SF_d,
    ADTS_SF_e,
    ADTS_SF_f
}sampling_frequency_index_e;

//adts固定头信息
typedef struct
{
    unsigned int syncword:12;           //帧同步标识一个帧的开始，固定为0xFFF
    unsigned int ID:1;                  //MPEG 标示符。0表示MPEG-4，1表示MPEG-2
    unsigned int layer:2;               //固定为'00'
    unsigned int protection_absent:1;   //标识是否进行误码校验。0表示有CRC校验，1表示没有CRC校验
    unsigned int profile:2;             //标识使用哪个级别的AAC。1: AAC Main 2:AAC LC (Low Complexity) 3:AAC SSR (Scalable Sample Rate) 4:AAC LTP (Long Term Prediction)
    unsigned int sampling_frequency_index:4;//标识使用的采样率的下标
    unsigned int private_bit:1;         //私有位，编码时设置为0，解码时忽略
    unsigned int channel_configuration:3;//标识声道数
    unsigned int original_copy:1;       //编码时设置为0，解码时忽略
    unsigned int home:1;                //编码时设置为0，解码时忽略
}fixed_header_t;

//adts可变头信息
typedef struct
{
    unsigned int copyrighted_id_bit:1;                  //编码时设置为0，解码时忽略
    unsigned int copyrighted_id_start:1;                //编码时设置为0，解码时忽略
    unsigned int aac_frame_length:13;                   //ADTS帧长度包括ADTS长度和AAC声音数据长度的和。即 aac_frame_length = (protection_absent == 0 ? 9 : 7) + audio_data_length
    unsigned int adts_buffer_fullness:11;               //固定为0x7FF。表示是码率可变的码流
    unsigned int number_of_raw_data_blocks_in_frame:2;  //表示当前帧有number_of_raw_data_blocks_in_frame + 1 个原始帧(一个AAC原始帧包含一段时间内1024个采样及相关数据)。
}variable_header_t;
}