[Mp4-tech] AAC decoder input buffer requirements

[Danijel Domazet]

Hi Barak,
6144 bits is maximum frame size per channel. If you have N channels than no
frame shall be larger than N*6144 - no matter what is inside this frame:
single channel elements, channel pair elements, fill elements, etc.
Daniel
----- Original Message ----- 
From: "Barak Zalstein" <Barak.Zalstein ceva-dsp.com>
To: <mp4-tech lists.mpegif.org>
Sent: Wednesday, December 21, 2023 2:18 PM
Subject: [Mp4-tech] AAC decoder input buffer requirements
Hello,
I'm trying to determine the required input buffer size for an HE-AAC
decoder.
According to 14496-3, 4.5.3 "The input buffer size is 6144 bits per SCE
or independently switched CCE, plus 12288 bits per CPE (6144*NCC). ".
Many decoder implementations (faad, helix, 3gp and various brochures of
closed source decoders) refer to this paragraph when declaring an input
buffer of 1536 bytes
(at least for decoding stereo).
However, it seems that this input buffer declaration does not take PCE,
DSE, and FIL elements size into consideration, which could cause a
larger requirement for the input frame size in the worst case.
My question is, since the size and quantity of the above elements is
unknown in advance, how should the input buffer size be decided, when
trying to support the largest possible frame size input. If "the largest
possible" is not a feasible requirement, what other criteria should be
used?
Barak.
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