geoffreyy/adts-reader

Rust reader for Audio Data Transport Stream (ADTS) frames

adts-reader

A Rust parser for the Audio Data Transport Stream framing format used to carry encoded AAC audio data.

👉 NB This is not an AAC decoder, nor is it able to parse the syntax of the AAC bitstream within the ADTS payload.

Calling code should,

• Provide an implementation of AdtsConsumer which will recieve callbacks as ADTS frame payloads are found
• Pass buffers containing ADTS data into the AdtsParser::push() method

Incremental parsing

The byte slice passed to push() need not end exactly at the boundry of an ADTS frame. Partial ADTS data remaining at the end of the given slice will be buffered internally in the parser, and the continuation of the ADTS data must be provided in the subsequent call to push(). This construction is intended to make it convinient to pass payloads of the individual MPEG Transport Stream packets in which ADTS data is commonly embedded, without having to pay the cost of reassembling entire PES packets.

Encoder configuration

ADTS frames include header data indicating the AAC encoder configuration, which will be made available to the calling code through the provided implementation of AdtsConsumer::new_config().

Configuration data is provided at stream start, and to simplify calling code the parser will only call AdtsConsumer::new_config() again if and when the audio configuration is found to change.

Supported ADTS syntax

• Fixed header fields
  • mpeg_version
  • protection
  • audio_object_type
  • sampling_frequency
  • private_bit
  • channel_configuration
  • originality
  • home
• Variable header fields data
  • copyright_identifier / copyright_number - deriving these values is not supported, since I've not seen any example bitstreams that use them
  • buffer_fullness
  • number_of_blocks
  • crc - not currently available (also, the CRC does not apply to all payload bytes; cyclic reduncancy check requires AAC bitstream parsing)
• AAC payload data
  • A &[u8] byte slice containing a complete ADTS frame payload (which might be composed of one or more AAC blocks, per number_of_blocks)