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I try to find any info about AAC HEv2 (PS) in an MPEG Transport Stream (TS) for HLS.

According to the HLS Authoring Specification for Apple Devices AAC HEv2 is a supported format. AAC HEv2 is part of MPEG-4, but I cannot understand how HEv2 could fit into a transport stream.

SBR (or HEv1) can be in TS by implicit signaling. In case of MP4 we have an audio specific config. But how can I multiplex AAC Parametric Stereo into the TS?

Is it available or not?
I cannot find any info from the Apple site and so on.

zx485
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Alexander Pastushkov
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    Every aac frame must have an adts header. – szatmary Feb 27 '18 at 17:42
  • For implicit signaling ADTS header has audio object type = LC. To detect HEv1 I need to find extension elements (EXT SBR DATA or EXT SBR DATA CRC) in bitstream. But what should I do with HEv2? ADTS header cannot help me for implicit signaling. – Alexander Pastushkov Feb 28 '18 at 03:04

1 Answers1

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There are two ways to put AAC into transport stream.

1. Using ADTS syntax (MPEG2-style).

In a such case PMT's stream_type should be specified as 0x0F (ISO/IEC 13818-7 Audio with ADTS transport syntax).

So, you are limited to using "old" (MPEG2) AAC versions only, without SBR and PS.

2. Using LATM+LOAS/AudioSyncStream syntax (MPEG4-style).

In a such case PMT's stream_type should be specified as 0x11 (ISO/IEC 14496-3 Audio with the LATM transport syntax).

And you can use all the force of "new" (MPEG4) AAC features, including SBR and PS.

Furthermore, DVB standard ETSI TS 101 154 demands: HEv1/HEv2 AAC shall be transmitted using LATM syntax.

dj_alek
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