AAC Audio Format (Pack AAC into Adts)

1, AAC

AAC (Advanced Audio Coding), Chinese name: Audio codec, which appeared in 1997, is based on MPEG-2. Co-developed by Fraunhofer IIS, Dolby Labs, T, Sony and other companies to replace the MP3 format. After the advent of the MPEG-4 standard in 2000, AAC re-integrates its features, adding SBR technology and PS technology to differentiate it from the traditional MPEG-2 AAC, also known as MPEG-4 AAC.

Syncword : The sync head is always 0xFFF, all bits must is 1, which represents the beginning of a Adts frame

ID: MPEG version:0 for MPEG-4, 1 for MPEG-2

Layer: Always: ' 00 '

Profile: Indicates which level of AAC is used, and some chips only support AAC LC. There are 3 types defined in MPEG-2 AAC:

Sampling_frequency_index: Represents the sample rate subscript used to find the value of the sample rate through this subscript in the sampling frequencies[] array.

There is supported frequencies:0:96000 Hz 1:88200 Hz 2:64000 Hz 3:48000 Hz 4:44100 Hz 5:32000 Hz 6:24000 Hz 7: 22050 Hz 8:16000 Hz 9:12000 Hz 10:11025 Hz 11:8000 Hz 12:7350 Hz 13:reserved 14:reserved 15:frequency is written explictly channel_configuration: Indicates the number of channels

0:defined in AOT specifc Config 1:1 channel:front-center 2:2 channels:front-left, front-right 3:3 channels:front-ce Nter, Front-left, Front-right 4:4 channels:front-center, Front-left, Front-right, Back-center 5:5 channels:front-cente R, Front-left, Front-right, Back-left, Back-right 6:6 channels:front-center, Front-left, Front-right, Back-left, Back-ri Ght, Lfe-channel 7:8 channels:front-center, Front-left, Front-right, Side-left, Side-right, Back-left, Back-right, LFE-c Hannel 8-15:reserved frame_length : The length of a Adts frame includes the Adts header and the AAC primitive stream.

buffer_fullness:0x7ff Description is a code stream with variable rate