如何在AAC原始流中添加ADTS头并进行解码播放

AAC原始流可以通过FFmpeg进行软解码或系统硬解码。为了简化处理，可以在流的前面添加ADTS头。ADTS头由7个字节组成，下面是生成ADTS头的示例代码，每次传递数据都以一个样本为单位：

uint8_t adts_header[7] = {0xff, 0xf9, 0x00, 0x00, 0x00, 0x1f, 0xfc};

// 设置AAC级别
switch (aac_level) {
    case AUDIO_AACM:
        adts_header[2] |= (0x00 <<6) & 0xc0;
        break;
    case AUDIO_AACL:
        adts_header[2] |= (0x01 <<6) & 0xc0;
        break;
    case AUDIO_AACS:
        adts_header[2] |= (0x02 <<6) & 0xc0;
        break;
    default: // 默认使用AACL
        adts_header[2] |= (0x01 <<6) & 0xc0;
        break;
}

// 设置采样率
switch (aac_sample_rate) {
    case SAMPLING_RATE_96000:
        adts_header[2] |= (0x00 <<2) & 0x3c;
        break;
    case SAMPLING_RATE_88200:
        adts_header[2] |= (0x01 <<2) & 0x3c;
        break;
    case SAMPLING_RATE_64000:
        adts_header[2] |= (0x02 <<2) & 0x3c;
        break;
    case SAMPLING_RATE_48000:
        adts_header[2] |= (0x03 <<2) & 0x3c;
        break;
    case SAMPLING_RATE_44100:
        adts_header[2] |= (0x04 <<2) & 0x3c;
        break;
    case SAMPLING_RATE_32000:
        adts_header[2] |= (0x05 <<2) & 0x3c;
        break;
    case SAMPLING_RATE_24000:
        adts_header[2] |= (0x06 <<2) & 0x3c;
        break;
    case SAMPLING_RATE_22050:
        adts_header[2] |= (0x07 <<2) & 0x3c;
        break;
    case SAMPLING_RATE_16000:
        adts_header[2] |= (0x08 <<2) & 0x3c;
        break;
    case SAMPLING_RATE_12000:
        adts_header[2] |= (0x09 <<2) & 0x3c;
        break;
    case SAMPLING_RATE_11025:
        adts_header[2] |= (0x0a <<2) & 0x3c;
        break;
    case SAMPLING_RATE_8000:
        adts_header[2] |= (0x0b <<2) & 0x3c;
        break;
    default: // 默认使用44100Hz
        adts_header[2] |= (0x04 <<2) & 0x3c;
        break;
}

// 设置声道数
switch (aac_channel_count) {
    case 1:
        adts_header[2] |= (0x01 >> 2) & 0x01;
        adts_header[3] |= (0x01 <<6) & 0xc0;
        break;
    case 2:
        adts_header[2] |= (0x02 >> 2) & 0x01;
        adts_header[3] |= (0x02 <<6) & 0xc0;
        break;
    case 3:
        adts_header[2] |= (0x03 >> 2) & 0x01;
        adts_header[3] |= (0x03 <<6) & 0xc0;
        break;
    case 4:
        adts_header[2] |= (0x04 >> 2) & 0x01;
        adts_header[3] |= (0x04 <<6) & 0xc0;
        break;
    case 5:
        adts_header[2] |= (0x05 >> 2) & 0x01;
        adts_header[3] |= (0x05 <<6) & 0xc0;
        break;
    case 6:
        adts_header[2] |= (0x06 >> 2) & 0x01;
        adts_header[3] |= (0x06 <<6) & 0xc0;
        break;
    case 8:
        adts_header[2] |= (0x07 >> 2) & 0x01;
        adts_header[3] |= (0x07 <<6) & 0xc0;
        break;
    default: // 默认使用2个声道
        adts_header[2] |= (0x02 >> 2) & 0x01;
        adts_header[3] |= (0x02 <<6) & 0xc0;
        break;
}

// 设置帧长度
adts_header[3] |= (aac_frame_length >> 11) & 0x03;
adts_header[4] = (aac_frame_length >> 3) & 0xff;
adts_header[5] |= ((aac_frame_length & 0x07) <<5);

通过上述代码，您可以根据实际的AAC流参数动态生成ADTS头，从而实现对AAC原始流的解码和播放。