Lossless watermarking of compressed media using reversibly decodable packets

Entropy coded multimedia signals such as JPEG and MPEG-1 and 2 have little or no error resiliency. To counter this situation, researchers have proposed using reversible VLCs (RVLC) to identify and limit error propagation. To bring error resiliency to Huffman-coded streams, a bidirectionally decodable packet has been introduced. This packet can be decoded in both directions to trap corrupted VLCs. Recognizing that watermark bits can be injected into the bitstream as forced bit errors, we have developed a watermarking algorithm around this decoder. The original decoder, however, is not able to track bit errors down to individual bits. We have developed an algorithm to restore the original unwatermarked bitstream. As a result of introducing watermark bits in the stream, serious synchronization issues arise at the decoder. The two-way decoding algorithm is capable of resolving and identifying existing resync markers and reestablishing synchronization. The algorithm has been successfully applied to several MPEG-2 video streams.