10 Enhanced aacPlus general audio codec: Compatibility

26.4013GPPEnhanced aacPlus general audio codecGeneral audio codec audio processing functionsGeneral descriptionRelease 17TS

Due to the modular approach the enhanced aacPlus encoder also includes a fully featured aacPlus and AAC-LC encoder.

A further consequence of the modular approach is decoder backwards compatibility: a Release-5 AAC decoder is able to decode the AAC part of an Enhanced aacPlus bitstream which contains both, SBR and Parametric Stereo data. However playback quality will be significantly limited. It is therefore recommended to not use this kind of compatibility unless it is specifically desired. Restricted backward compatibility can be accomplished by selecting the appropriate signalling as described in [6].

Table 1 illustrates the bitstream and decoding compatibilities as outlined above.

Table 1: Playback capabilities of decoders

		Decoder
		Enhanced aacPlus		Release-5 AAC-LC, backwards compatible signalling	Release 5 AAC-LC, non backwards compatible signalling
Encoder mode	Enhanced aacPlus stereo, at and below 44 kbit/s	Yes		Mono only, no SBR	No
	Enhanced aacPlus mono or stereo above 44 kbit/s	Yes		No SBR	No
	Release 5 AAC-LC	Yes		Yes	Yes

Note: the table does not contain information on AAC-LTP, which is an optional audio codec since Release 5.