Re: Mp3 Encoding

Quoting Ajay Mandlekar <[email protected]> (from Tue, 20 Mar  
2012 13:13:09 -0700):

> Hello,
>
> My partner and I are both high school students who are working on a
> device that encrypts secret messages into sound files. The method that
> we are using involves the conversion of data into an mp3 format, and
> this results in a loss of data that is crucial to the success of the
> device. We would like to be able to predict which points are going to
> be modified significantly or lost completely when we write our data as
> an mp3. Could you help us?
>
> We were able to achieve success with .flac files (since they're a
> lossless audio format), but with mp3 files, were unable to recover the
> secret message since the mp3 compression altered the data points. We
> were thinking that if we could know which points (in the time domain)
> would be adversely affected, we could avoid those points. Any
> clarification on how .mp3 files compress data would be very helpful.
> Thank you!

The generic answer is: you can't predict what _any_ MP3 encoder will  
throw away and what not. They are free to throw away anything. It  
depends upon the bitrate, the encoding options, and off course on  
which software is used to encode the MP3. A different encoder shows  
different behavior.

The LAME specifc answer is: well, look at the source, it's too complex  
to explain in some words.

As a generic advise, do not put the important bits together (have  
enough space between them, not only in the time domain, but also in  
the frequency domain). But this simple advise will only work if you  
only have your data in the MP3 file, and nothing else. If you want to  
use steganography this simple advise will not work.

Bye,
Alexander.

-- 
Loneliness is a terrible price to pay for independence.

http://www.Leidinger.net    Alexander @ Leidinger.net: PGP ID = B0063FE7
http://www.FreeBSD.org       netchild @ FreeBSD.org  : PGP ID = 72077137


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