[Mp4-tech] AAC - CRC protection

[Alexander Groeschel]

Hi Danijel,
I am afraid you are right, the literal interpretation is to feed some data 
twice in this case. An attempt to change this (probably unwanted stuff) in 
MPEG came too late (chips were out at that time already).
best,
alex.
mp4-tech-bounces lists.mpegif.org wrote on 09/05/2024 12:38:40 PM:
> 
> Hi all,
> 
> One problem regarding AAC audio with ADTS header that uses CRC 
protection.
> 
> ISO 14496-3 states:
> "...first 192 bits of any channel_pair_element should be CRC protected. 
In 
> addition, the first 128 bits of 2nd individual_channel_stream in the 
> channel_pair_element must be protected.
> For any element where the specified protection length of 128 or 192 bits 

> exceeds its actual length, the element is zero padded to the specified 
> length for CRC calculation."
> 
> 
> What happens when CPE is very short (~50 bits)? By feeding 192 bits of 
CPE 
> to the CRC I will protects 2nd ICS in this CPE automaticaly. Do I then 
feed 
> 2nd ICS again into CRC calculator, this time as 128 bits?
> 
> 
> Thanks,
> Danijel Domazet
> 
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_________________________________
Alexander Gröschel
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