MATLAB: How to convert bitstream to packets and bitxor function

bit-streamvideovideo processing

I have to convert a bit stream file such as name `BL.264` source file . Now I want to parse the file into packets with packet size is 50 bytes. After that, I want to implement bit XOR between first packet and second packet. To do it, I will use `fread` and `bitxor` functions. However, I have some issues:
  1. If size of file is not divisible by packet sizes, we must add some padding at the end of final packet, *Right?* Let see my implementation, is it correct?
  2. The bitxor supports xor bitwise that have limit length. In my case, packet size is 50 bytes, it is impossible to bitxor two packet. How to resolve that problem.
Let see my code. If have any problem, let me know
function packet=bitstream2packet(file,psize)
      %%file='BL.264';
      %%psize=50;
      fid=fopen(file,'r');
      bytelist=fread(fid,'*uint8')';    
      bitexpanded = dec2bin(bytelist(:), 8) - '0';     
      bitstream = reshape( bitexpanded.', [],1);
      %%Add padding
      remain=rem(size(bitstream,1),psize);
      bitstream(end+psize-remain)=0;
      packet = reshape( bitstream.', [],50);
      xorPacket=bitxor(packet(1,:),packet(2,:))
      fclose(fid);
end

Best Answer

You're storing your bitstream as a logical array. In that case, it's a logical operation that you want to perform, not a bitwise xor. Therefore use xor instead of bitxor.
Compare
n1 = 8; n2=32
n1logicalbit = dec2bin(n1, 8) - '0';  %gives [0 0 0 0 1 0 0 0]
n2logicalbit = dec2bin(n2, 8) - '0';  %gives [0 0 1 0 0 0 0 0]
logicalxor = xor(n1logicalbit, n2logicalbit); %gives [0 0 1 0 1 0 0 0]
binaryxor = bitxor(n1, n2); %gives 40
isequal(logicalxor, dec2bin(binaryxor, 8)-'0') %return true
Otherwise your code is fine. There's a few unnecessary transpositions, you could simply do:
bytelist = fread(fid, '*uint8'); %no transpose
bitexpanded = dec2bin(bytelist, 8) -'0'; %no colon which in your case just transposed
I would also move the fclose to just after you've done the fread. This way if your code stops further down because of an error or the user interrupting it, the file won't be left open.
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