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Stefan Westerfeld
audiowmark
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b050d32e
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b050d32e
authored
Feb 08, 2019
by
Stefan Westerfeld
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Documentation updates (mostly about watermark strength).
Signed-off-by:
Stefan Westerfeld
<
stefan@space.twc.de
>
parent
0e916fe8
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b050d32e
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@@ -51,6 +51,36 @@ 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
== Watermark Strength
The watermark strength parameter affects how much the watermarking algorithm
modifies the input signal. A stronger watermark is more audible, but also more
robust against modifications. The default strength is 10. A watermark with that
strength is recoverable after mp3/ogg encoding with 128kbit/s. In our informal
listening tests, this setting also has a very good subjective quality.
A higher strength (for instance 15) would be helpful for instance if robustness
against multiple conversions or conversions to low bit rates (i.e. 64kbit/s) is
desired.
A lower strength (for instance 6) makes the watermark less audible, but also
less robust. Strengths below 5 are not recommended. To set the strength, the
same value has to be passed during both, generation and retrieving the
watermark. Fractional strengths (like 7.5) are possible.
audiowmark add --strength 15 in.wav out.wav 0123456789abcdef0011223344556677
audiowmark get --strength 15 out.wav
Since the watermark modifies the input signal, it will make it louder at some
positions. To avoid clipping, the input signal is scaled down during
watermarking. For the strength values mentioned here everything should work,
however for very strong watermarks you are likely to see a warning like this
audiowmark: warning: clipping occured in watermarked audio signal
which can be fixed by modifying the scaling factor (which defaults to
0.95) using `--pre-scale 0.9`.
== Dependencies
If you compile from source, audiowmark needs the follwing libraries:
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@@ -59,6 +89,7 @@ If you compile from source, audiowmark needs the follwing libraries:
* libsndfile
* libgcrypt
* libzita-resampler
* libmpg123
== Building fftw
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