[Mp4-tech] [Audio] Erroneous bit streams...

[guhapriya ganapathy]

Hi Umang,
  That being the case, why aren't there any erroneous bitstreams available in the market to validate the robustness of the decoder? Only CT provides a set of erroneous bitstreams for SBR part of HEAAC as a part of its certification package. 
  As such, ISO has no erroneous bitstreams for AAC.
  Regards,
  Guha Priya.
Umang Garg <ugarg neomagic.com> wrote:
      Guha, Sris
  While HEAAC for broadcast environments mandates the CRC check in ADTS format, it usage appears to be quite redundant with little practical advantage. It existence may have more to do with legacy reasons. 
  The redundancy arises from the fact that the CRC validation of the  bitstream cannot happen untill the stream has been parsed upto a specified number of bits. If the bitstream is corrupted in the 'right' places then it is possible that the parsing process can go haywire. This implies that you may not interpret the bits correctly and the parsing may take a completely different control flow path. It is a chicken-and-egg situation.
  Your best bet lies in the ability to handle serious corruption issues at network level. Minor bitstream distortions can then be handled inside the decoder by having a robust error handling mechanism along with CRC check.
  Regards,
  Umang 
---------------------------------
  From: mp4-tech-bounces lists.mpegif.org [mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of %Sriskanthan Nadarajah
Sent: Monday, May 22, 2024 8:20 PM
To: guhapriya ganapathy; mp4-tech lists.mpegif.org
Subject: RE: [Mp4-tech] [Audio] Erroneous bit streams...
        Hi Guha Priya.
  The CRC should be checked and error passed before passing  the stream to the Codec. 
      Sris
  WINUX Interfacing Technology Pte. Ltd.
  Tele: (65) 6794-3069 H/P 92763116
  Com. Reg. No: 200303307W
  www.winux-it.com
---------------------------------
  From: mp4-tech-bounces lists.mpegif.org on behalf of guhapriya ganapathy
Sent: Mon 5/22/2006 1:45 PM
To: mp4-tech lists.mpegif.org
Subject: RE: [Mp4-tech] [Audio] Erroneous bit streams...
    Hi Umang,
  In case of a packet loss, it is fine. We may have to make our own decisions. 
  Coming to bitstream corruption, what is the probability of the corrupted bitstream reaching the codec? When a corruption is detected at the network layer by the CRC, is it being dropped? If so, what is the need for CRC in the codec?
  Regards,
  Guha Priya.
Umang Garg <ugarg neomagic.com> wrote:
    Hello Guha, 
  In broadcast environment you may encounter packet loss and stream corruption as two primary errors. 
  For HEAAC:
  Stream corruption may be checked via CRC. ADTS format has a CRC check along with a separate CRC check for SBR decoding.
  Similarly, packet loss may also have to be handled gracefully within the decoder. In case of a loss of frame(s) the simplest technique is insertion of a silence frame (to maintain synchronization) but a more appropriate technique would be gradual muting.  As far as I know, the HEAAC standard does not say much about packet loss in general or the muting technique in particular. You may have to make your own decisions on that.
  Regards,
  Umang  
---------------------------------
  From: mp4-tech-bounces lists.mpegif.org [mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of guhapriya ganapathy
Sent: Thursday, May 18, 2024 5:19 PM
To: mp4-tech lists.mpegif.org
Subject: [Mp4-tech] [Audio] Erroneous bit streams...
  Dear all,
  Suppose you have an audio codec which is a part of a broadcast system (any system for that matter). What are the possible errors that might creep in the bitstream when it reaches the decoder? (There will be CRC check for each packet in the network layer, but I am concerned about the bitstream when it reaches the decoder.. what are the chances that the bit stream is corrupted?) 
  Taking AAC HE as an example, Coding Technologies provides erroneous bitstreams for SBR (although SBR has CRC check) as a part of its certification package (wherein for example one bit in every third frame is corrupted – a random corruption!), whereas ISO does not(?) provide erroneous bitstreams. Of what value are erroneous bitstreams to the decoder? Is there a value add in generating erroneous bitstreams for decoders? If so, what is the approach so that it matches what happens in the real time?
  Regards,
  Guha Priya.
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