ADTS

Audio Data Transport Stream (ADTS) is a format, used by MPEG TS or Shoutcast to stream audio, usually AAC.

Structure

Header consists of 7 or 9 bytes (with or without CRC).

• 12 bits of syncword 0xFFF, all bits must be 1
• 1 bit of field ID. 0 for MPEG-4, 1 for MPEG-2
• 2 bits of MPEG layer. If you send AAC in MPEG-TS, set to 0
• 1 bit of protection absense. Warning, set to 1 if there is no CRC and 0 if there is CRC
• 2 bits of profile code. The MPEG-4 Audio Object Type minus 1
• 4 bits of sample rate code. MPEG-4 Sampling Frequency Index (15 is not allowed)
• 1 bit of private stream. Set to 0
• 3 bits of channels code. MPEG-4 Channel Configuration (in the case of 0, the channel configuration is sent via an inband PCE)
• 1 bit of originality. Set to 0
• 1 bit of home. Set to 0
• 1 bit of copyrighted stream. Ignore it on read and set to 0
• 1 bit of copyright start. Set to 0
• 13 bits of frame length. This value must include 7 or 9 bytes of header length: FrameLength = (ProtectionAbsent == 1 ? 7 : 9) + size(AACFrame)
• 11 bits of some data. unknown yet
• 2 bits of frames count in one packet. Set to 0
• aac frame going.

Usage in MPEG-TS

ADTS packet must be a content of PES packet. Pack AAC data inside ADTS frame, than pack inside PES packet, then mux by TS packetizer.

Usage in Shoutcast

ADTS frames goes one by one in TCP stream. Look for syncword, parse header and look for next syncword after.