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Topic: Extraction of MDCT coefficients on MP3 or WAV previously compressed (Read 5967 times) previous topic - next topic
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Extraction of MDCT coefficients on MP3 or WAV previously compressed

Hi,

I'm doing a master's on detection of double compression on MP3 audio files. I need to extract the MDCT (Modified Discrete Cosine Transform) coefficients of MP3 file or WAV previously compressed. The related work that i found utilized the LAME MP3 ( http://sourceforge.net/projects/lame/ ) encoder to do that extraction, but i found it's very difficult to use for that objective. There is a minimal documentation on the file HACKING of the link. It only describes that is possible to compute the MDCT coefficients, but i don't know how to do it.
 
I appreciate any help

Extraction of MDCT coefficients on MP3 or WAV previously compressed

Reply #1 –
If you want to record the MDCT coefficients during encoding, I would just add an fwrite() right after the call to the MDCT and store the transformed buffer directly to disk.

Extraction of MDCT coefficients on MP3 or WAV previously compressed

Reply #2 –
Quote from: saratoga on
If you want to record the MDCT coefficients during encoding, I would just add an fwrite() right after the call to the MDCT and store the transformed buffer directly to disk.


I'm new on understanding the code of MP3. I need to extract the MDCT coefficients before the quantization. Example: I have WAV file previously compressed. On that audio i only want to extract the MDCT coefficients before quantization or huffman encoding. I don't want to compress the audio again. I only need the coefficients of each frame separated.

Extraction of MDCT coefficients on MP3 or WAV previously compressed

Reply #3 –
Quote from: rodca1986 on
Example: I have WAV file previously compressed. On that audio i only want to extract the MDCT coefficients before quantization or huffman encoding.


WAV files don't have MDCT coefficients.  Do you mean you have an MP3 file rather than a WAV file?  Or something else? 

Quote from: rodca1986 on
I don't want to compress the audio again. I only need the coefficients of each frame separated.


I don't fully understand the question, but I think the answer is to edit an [encoder/decoder] such that it saves the MDCT coefficients right [after/before] the MDCT.