mirror of https://git.FreeBSD.org/ports.git
16 lines
818 B
Plaintext
16 lines
818 B
Plaintext
A sound file 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 bitrate 128 kbit/s or higher), 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. The signal is split into 1024 sample
|
|
frames. For each frame, some pseoudo-randomly selected amplitudes of the
|
|
frequency bands of a 1024-value FFTs are increased or decreased
|
|
slightly, which can be detected later.
|