1. VIDEO CODEC USING MATLAB
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H.264 BASELINE CODEC V2
This sample assignment shows slightly updated version 2 of H.264 baseline codec.
dec_cavlc(bits,nL,nU)
function [data,i] = dec_cavlc(bits,nL,nU)
%% CAVLC Decoder
% By A. A. Muhit
% It takes bitstream and decodes 4x4 block of data
% Load the table containing all the tables
% load table.mat;
global Table_coeff0 Table_coeff1 Table_coeff2 Table_coeff3
global Table_run Table_zeros
% test data
% bits =
'00000000001000101000000011001011111001011101010000000010000111111111111111001110';
% nL = 0;
% nU = 0;
% find n parameter (context adaptive)
if (nL>0)&(nU>0)
n = (nL + nU)/2;
elseif (nL>0)|(nU>0)
n = nL + nU;
else
n = 0;
end
% Coeff_token mapping
% Rows are the total coefficient(0-16) and columns are the trailing ones(0-3)
% TABLE_COEFF0,1,2,3 ARE STORED IN TABLE.MAT OR CAVLC_TABLES.M FILE
% Choose proper Table_coeff based on n value
if 0<=n<2
Table_coeff = Table_coeff0;
elseif 2<=n<4

2. Table_coeff = Table_coeff1;
elseif 4<=n<8
Table_coeff = Table_coeff2;
elseif 8<=n
Table_coeff = Table_coeff3;
end
i = 1;
coeff_token = '';
% Find total coefficients and trailing ones
while (i<=length(bits))
coeff_token = [coeff_token bits(i)];
x = strcmp(Table_coeff,coeff_token);
[r,c]=find(x==1);
i = i + 1;
if (r>0)&(c>0)
break;
end
end
% Find total coefficients and trailing ones
i_total = r - 1;
i_trailing = c - 1;
% if no coefficients return 4x4 empty blocks of data
if i_total==0
data = zeros(4,4);
return;
end
k = 1;
m = i_trailing;
while m>0
if bits(i)=='0'
level(k)=1;
elseif bits(i)=='1'
level(k)=-1;
end
k = k + 1;
m = m - 1;
i = i + 1;
end
%% Decode the non-zero coefficient/level values
if (i_total>10)&(i_trailing<3)
i_sufx_len = 1;

3. else
i_sufx_len = 0;
end
while k<=i_total
% Decode level prefix
[level_prfx,i]= dec_prfx(bits,i);
% Decode level suffix
level_sufx_size = 0;
if (i_sufx_len>0)||(level_prfx>=14)
if (level_prfx==14)&(i_sufx_len==0)
level_sufx_size = 4;
elseif level_prfx>=15
level_sufx_size = level_prfx - 3;
else
level_sufx_size = i_sufx_len;
end
end
if level_sufx_size==0
level_sufx = 0;
else
sufx = bits(i : i + level_sufx_size -1);
level_sufx = bin2dec(sufx);
i = i + level_sufx_size;
end
i_level_code = bitshift(min(15,level_prfx),i_sufx_len) + level_sufx;
if (level_prfx>=15)&(i_sufx_len==0)
i_level_code = i_level_code + 15;
end
if level_prfx>=16
i_level_code = i_level_code + (bitshift(1,level_prfx - 3) - 4096);
end
if (k == i_trailing + 1)&(i_trailing<3)
i_level_code = i_level_code + 2;
end
if rem(i_level_code,2)==0 % i_level_code is even
level(k) = bitshift(i_level_code + 2,-1);
else % odd number
level(k) = bitshift(-i_level_code - 1, -1);
end
if i_sufx_len==0

4. i_sufx_len = 1;
end
if ((abs(level(k)))>bitshift(3,i_sufx_len - 1))&(i_sufx_len<6)
i_sufx_len = i_sufx_len + 1;
end
k = k + 1;
end
%% Decode total zeros
s='';
i_total_zero = 0;
if i_total==16
i_zero_left = 0;
else
while (i<=length(bits))
s = [s bits(i)];
x = strcmp(Table_zeros(i_total,:),s);
r = find(x==1);
i = i + 1;
if r>0
i_total_zero = r-1;
break;
end
end
end
%% Decode run information
i_zero_left = i_total_zero;
j=1;
ss = '';
run = zeros(1,length(level));
while i_zero_left>0
while (j<i_total)&(i_zero_left>0)
ss = [ss bits(i)];
i_zl = min(i_zero_left,7);
x = strcmp(Table_run(:,i_zl),ss);
r = find(x==1);
i = i + 1;
if r>0
run(j)=r-1;
i_zero_left = i_zero_left - run(j);
j = j + 1;

5. ss = '';
end
end
if i_zero_left>0
run(j)=i_zero_left;
i_zero_left = 0;
end
end
%% Combine level and run information
k = i_total + i_total_zero;
l = zeros(1,16);
while k>0
for j=1:length(level)
l(k)=level(j);
k = k - 1;
k = k - run(j);
end
end
%% Reorder the data into 4x4 block
scan = [1,1;1,2;2,1;3,1;2,2;1,3;1,4;2,3;3,2;4,1;4,2;3,3;2,4;3,4;4,3;4,4];
for k=16:-1:1
m=scan(k,1);
n=scan(k,2);
data(m,n)=l(k); % l contains the reordered data
end
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