[CELT-dev] Scanning the compressed celt for an artifact

Andrew Lentvorski bsder at allcaps.org
Sat Jul 16 17:51:00 PDT 2011

I need to test the latency of a system that I ported CELT to.  I'd like 
to set a flag when the stream "changes".

In order to see the stream "change", I'd like to be able to scan the 
compressed CELT directly to set the flag.  ie.  I'd like to be able to 
find a byte or two that change reliably between two values when the 
stream "changes".  I don't want to have to decompress the CELT and then 
analyze the PCM (that would take too long given the CPU power available).

I can construct the streams to change in a way that would make the 
compressed CELT change in an easily detectable way.

My first thought was simply to build a stream that consists of two tones 
separated sufficiently in frequency.  Since CELT encodes power into 
bins, there should basically be a few numbers somewhere that should 
exhibit a very large magnitude change if I do this.

The only difficulty is that I would have to dig very deep into the 
source code to figure out whether this was A) possible and B) what bytes 
in the compressed bitstream change

Can anybody with more CELT knowledge than me give me some pointers?


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