Fhg's "inverse Decoder" - Or Encoder Detector Options

[Ivan Dimkovic]

I've just read interesting AES article (#5256) regarding FhG's "Inverse Decoder" tool..

It seems that this tool is able to:

- Analyse the encoding window size (1152 / 1024 / ... samples)
- Analyse the short block usage
- Analyse the bit reservoir usage
- Analyse the M/S and I/S usage
- Analyse the quantization step size
- Analyse the TNS usage

With this information, they could detected what algorithm was used, and with database of known properties - what encoder and version, as well as encoding settings were used only by analysing of decoded PCM file!!

This is very interesting and straightforward algorithm for transcoding without losses, and they claim that they can even reconstruct MP3/AAC bitstream out of decoded WAV without degradation of sound quality!

But, there are some other usages, like this:

The increasing popularity of low bitrate audio coding schemes comes along with a significant number of undesirable activities, such as the illegal distribution of copyrighted audio over the Internet and the availability of encoders illicitly using patented algorithms. In this context, the inverse decoder can be an interesting tool both for forensic purposes as well as for investigations about violations of IPRs.

So, the tool could be used for detecting unlicensed MP3 and AAC encoders, or illegally obtained MP3 encoders

[Ivan Dimkovic]

Hehe, right :-)

And, as far as I understand - some companies are distributing LAME legally (by paying $15k/yr) and therefore FhG could never tell was the distributed LAME encoding "legal" or not