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Stefan Westerfeld
audiowmark
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244953dd
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244953dd
authored
Feb 03, 2019
by
Stefan Westerfeld
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Added basic documentation.
Signed-off-by:
Stefan Westerfeld
<
stefan@space.twc.de
>
parent
78e5c8eb
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244953dd
= audiowmark - Audio Watermarking
= audiowmark - Audio Watermarking
(TODO)
== Description
`audiowmark` is an Open Source solution for audio watermarking. A sound file
(typically wav) is read by the software, and a 128-bit message is stored in a
watermark in the output sound file. For human listeners, the files typically
sound the same.
However, the 128-bit message can be retrieved from the output sound file. Our
tests show, that even if the file is converted to mp3 or ogg (with bitrates
higher than 128 kbit/s), the watermark usually can be retrieved without
problems. The process of retrieving the message does not need the original
audio file (blind decoding).
Internally, audiowmark is using the patchwork algorithm to hide the data in the
spectrum of the audio file. Some pseoudo-randomly selected amplitudes of the
frequency bands of a 1024-value FFTs are increased or decreased slightly, which
can be detected later. The algorithm used here is inspired by
Martin Steinebach: Digitale Wasserzeichen für Audiodaten.
Darmstadt University of Technology 2004, ISBN 3-8322-2507-2
== Adding/Retrieving a Watermark
To add a watermark to the soundfile in.wav with a 128-bit message (which is
specified as hex-string):
audiowmark add in.wav out.wav 0123456789abcdef0011223344556677
To get the 128-bit message from the watermarked file, use:
audiowmark get out.wav
== Watermark Key
Since the software is Open Source, a watermarking key should be used to ensure
that the message bits cannot be retrieved by somebody else (which would also
allow removing the watermark without loss of quality). The watermark key
controls all pseudo-random parameters of the algorithm. This means that
it determines which frequency bands are increased or decreased to store a
0 bit or a 1 bit. Without the key, it is impossible to decode the message
bits from the audio file alone.
Our watermarking key is a 128-bit AES key. A key can be generated using
audiowmark gen-key test.key
and can be used for the add/get commands as follows:
audiowmark add --key test.key in.wav out.wav 0123456789abcdef0011223344556677
audiowmark get --key test.key out.wav
== Building fftw
== Building fftw
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