Help please! Parsing the compressed video stream

[xujyo]

My thesis is about information hiding in compressed video stream. Now I have to parse the bitstream data of the compressed video, and obtain the DCT coefficients or the motion vectors and so on. Only in this way, I can modify the coefficients or motion vectors, and lastly write the modified data back into the compressed bitstream.
But I don't know how to get the compressed data like DCT coefficients or motion vectors. Could you please tell me is there any tools or algorithms can do this?

Thank you very much!

[Guest]

With the MPEG2 specification and source code examples of parsing you should have what you need. The spec is here:

http://neuron2.net/library/mpeg2/iso13818-2.pdf

There are many source code examples available. You could start with the MPEG2 parser in ffdshow, for example. There is also code in DGMPGDec, VirtualDub MPEG2, etc.

[xujyo]

Thank you! neuron2!
Do you know are there any algorithms that write by Matlab can realize my demand?

[xujyo]

Actually, my question is about how to get the DCT coefficients and motion vectors or others from the compressed video stream, modifying them and write the modified data back into the video stream.

[Guest]

You'll mess up the video if you do that.