MPEG-4 AAC Format

AAC封裝主要分三類

1. Multiplex (LATM, M4Mux)
2. Storage(MPEG-4 FileFormat, ADIF)
3. Transmission (ADTS, LOAS)
   

AAC的SDP裡的
AudioSpecificConfig: (ISO/IEC 14496-3, Table1.13)

5 bits: object type

4 bits: frequency index
if (frequency index == 15)
24 bits: frequency
4 bits: channel configuration
1 bit: frame length flag
1 bit: dependsOnCoreCoder
1 bit: extensionFlag

ref:

• Understanding AAC RFC 3016 - RTP Payload Format for MPEG-4 Audio/Visual Streams
• RFC 3640 - RTP Payload Format for Transport of MPEG-4 Elementary Streams
• ISO/IEC 14496-3
• Session Description Protocol