insert_wm.m

Digital watermarking

function [input_string,out] = insert_WM(input,blk,alpha,WM)
% This function will insert the watermark int he input 
% audio stream. The input variable are
% input = input audio stream
% block = input stream is divided into segments of equal length of size block
% alpha = strength of the watermark
% WM = randomly generated watermark

len_input = length(input);
len_WM = length(WM);
% DIVIDE THE WHOLE STREAM IN TWO PART 
% ONE IS MULTIPLES OF BLOCK AND
% OTHER IS RESIDUAL OF INPUT
residue_of_input =  mod(len_input,blk);
% ZERO PADDING IN ORDER TO FIX THE SIZE OF EACH SEGMENT
input_string = [input zeros(1,blk-residue_of_input)];
% TOTAL NO OF SEGMENTS
no_of_segments = len_input/blk;

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% FFT OF EACH SEGMENT AND THEN CONCATINATE ALL THESE SEGMEMTS
FFT_of_input_string = (blkproc(input_string,[1 blk],'fft'));
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% INSERTION OF WTERNARKING %

abs_FFT_of_input_string = (FFT_of_input_string);
out_string = abs_FFT_of_input_string;

for i=1:len_WM
   	[g,m] = max(abs_FFT_of_input_string);
   	out_string(m) = out_string(m).*(1 + alpha.*WM(i));
   	abs_FFT_of_input_string(m) = 0;
end
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% INVERSE FFT OF THE WATERMARKED STREAM
out = (blkproc(out_string,[1 blk],'ifft'));
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