AFOSR PROGRAM REVIEW DATA HIDING IN COMPRESED DIGITAL VIDEO

1. AFOSR PROGRAM REVIEWDATA HIDING IN COMPRESED DIGITAL VIDEO Bijan Mobasseri, PI Dom Cinalli, Aaron Evans, Dan Cross, Sathya Akunuru ECE Department Villanova University Villanova, PA 19085 June 6-8, 2002 Burlington, VT

2. Outline • Data hiding/watermarking requirements • Data hiding in compressed video • Using variable length codes for data hiding • Lossless watermarking using resilient-coding • Video authentication through self-watermarking • Metadata embedding • Open Issues 2002 AFOSR Program Review

3. Background • This effort is funded by AFOSR to develop algorithms for the creation of smart digital videos • The project is monitored by AFRL/IFEC • Applications include • Watermarking for tamper detection, recovery • Data hiding for covert communications • Metadata embedding • Security and access control 2002 AFOSR Program Review

4. Data hiding requirements • Data hiding must at least meet the following three conditions: • Transparency • Robustness or fragility • Security • Places to hide data are: • Spatial- pixel amplitudes, LSB, QIM • Transform domain- spread spectrum, Fourier/wavelet, LPM • Joint- time/frequency distribution 2002 AFOSR Program Review

5. State of video watermarking • Video watermarking is strongly influenced by still image watermarking algorithms where video is modeled as a sequence of stills • Examples include LSB watermarking of raw frames, spread spectrum and 3D-DFT • Increasingly, however, the native state of video is in compressed format and does not yield itself to simple still frame modeling 2002 AFOSR Program Review

6. The medium • Understanding the medium is a prerequisite to watermarking it • Uncompressed NTSC video runs at 168 Mb/sec. MPEG-2 runs at <10 Mb/sec.; a 96% reduction • Redundancy is at the heart of data hiding. Compressed video leaves precious little space to hide data while maintaining robustness, security and imperceptibility 2002 AFOSR Program Review

7. Distinction with a difference • We recognize a difference between • watermarking of compressed video vs. • compressed video watermarking • The former refers to watermarking of video which may later be compressed • The later refers to watermarking that is done entirely post-compression. 2002 AFOSR Program Review

8. MPEG bitstream syntax 2002 AFOSR Program Review

9. DATA HIDING IN VLCs

10. Label-carrying VLCs • Variable length codes are the lynchpin of MPEG • There is a subset of MPEG VLC codes that represent identical runs but differ in level by just one From: Langelaar et al, IEEE SP Magazine September 2000 2002 AFOSR Program Review

11. Data hiding in lc-VLC • The algorithm proposed by Langelaar embeds watermark bits in the LSB of the level of the lc-VLCs 2002 AFOSR Program Review

12. Data hiding capacities:data 2002 AFOSR Program Review

13. Lossless video watermarking using error-resilient VLCs* *B. Mobasseri, “Watermarking of Compressed Multimedia using Error-Resilient VLCs,” MMSP02- in review

14. The idea:watermark as intentional bit errors • There has been notable cross currents of late between watermarking and channel coding • A close look reveals that watermarking of VLCs is essentially equivalent to channel errors. • Bit errors and watermark bits have identical impact. They both cause bit errors in affected VLCs. • The difference is that channel errors occur randomly whereas watermark bits can be planted at will and at locations that facilitate detection. 2002 AFOSR Program Review

15. The solution-lossless watermarking • Embed watermark bits in the VLCs as controlled bit errors • MPEG-2 VLCs, however, have no inherent error protection. Any bit error will cause detection failure up to the next resynchronization marker • Bidirectionally decodable codewords are capable of isolating and reversing channel errors • An interesting side effect of the above hypothesis is that if error-resilient VLCs are successful in reversing bit errors, the outcome would be mathematically lossless watermarking 2002 AFOSR Program Review

16. Two-way decodable VLCs • MPEG-4 uses RVLCs but Girod(1999) has proposed an elegant design whereby conventional VLCs are made to exhibit resynchronizing property • To construct resynchronizing VLCs from ordinary VLCs, we first define a packet consisting of N consecutive VLCs vlc’=fliplr(vlc) 2002 AFOSR Program Review

17. Code structure • Each VLC is represented twice in the new bitstream. It is this property that allows error resiliency • Burst error shall not be so long to simultaneously affect the same bit of identical VLC 2002 AFOSR Program Review

18. Watermarking using bidirectional codes VLCs: Message:{a,b,d,c} Bidirectional VLC Watermarked w={w1,w2,w3,w4) bidirectional VLC 2002 AFOSR Program Review

19. Watermark detection • On forward decoding, vlc_a and vlc_b will be correctly decoded. Failure will occur at vlc_d • On forward direction, correctly decoded symbols are {a,b}. On reverse decoding, correctly decoded symbols are {c,d}. • The last symbol correctly decoded on the reverse path is the same symbol that failed detection on forward decoding. The correct symbols are then {a,b,d,c} 2002 AFOSR Program Review

20. Distance properties • Each VLC in the C stream appears twice. Therefore, the ith bit of a VLC is separated from its copy by  bits given by • If the watermark burst begins with the last bit(LSB) of the VLC, the burst cannot last longer than minbits. 2002 AFOSR Program Review

21. Watermarking capacity • Watermarking capacity of a VLC falls under two categories • L=l, in this case C=L bits/packet • L>l, watermark burst may cross over to the L-l bits of the next VLC. It follows that 2002 AFOSR Program Review

22. Implementation 2002 AFOSR Program Review

23. SELF-WATERMARKING* *D. Cross, B. Mobasseri, “Watermarking for self-authentication of compressed video,” IEEE ICIP2002, September 22-25, 2002, Rochester, NY.

24. Self-watermarking:the concept • In self-watermarking, the watermark is extracted from the source itself • Self-watermarking prevents watermark pirating and may allow recovery of tampered material such as cut and paste or re-indexing attacks • Most work on self-watermarking has been done on images. If it has been done video, the approach is to model video as a sequence of stills 2002 AFOSR Program Review

25. Self-watermarking of compressed video Scramble (key) Bit extraction I-frame 1 0 VLC (0,5) VLC (0,16) VLC (1,15) VLC (0,6) VLC (1,10) VLC (1,11) VLC (0,12) NEXT GOP 2002 AFOSR Program Review

26. Watermark extraction • Watermark is extracted from the I frame by zigzag scanning of I frame VLCs and storing in array w • The number of bits in w must be less than or equal to the number of lc-VLCs in gop. In addition, w must contain integer number of VLCs 2002 AFOSR Program Review

27. Watermark embedding • To be able to fully embed the I frame into the GOP the following must hold • Once the mask is generated, the embedding method is as follows 2002 AFOSR Program Review

28. Data 2002 AFOSR Program Review

29. Watermarking capacity • I frames hold almost all of the watermark data. These results are expected since only the intra-coded macroblocks will hold watermark data. 2002 AFOSR Program Review

30. Metadata Embedding

31. Background • Video images & metadata recorded and handled as two separate streams • Storage overhead • Bookkeeping issues • Accuracy and human error • Cumbersome to display • It would be nice to permanently attach metadata to video and make it available during playback Metadata Video 2002 AFOSR Program Review

32. Metadata Watermarking MPEG Encoder Video Buffer Display Watermarked Video Metadata Buffer W Store Watermarking system combines both video and metadata feeds to form a single, less cumbersome stream that can be both displayed and stored. 2002 AFOSR Program Review

33. Real-Time Processing Metadata is embedded into MPEG video during the recording process and is available for immediate transmission from UAV. Batch Processing Video & metadata recorded in their entirety before embedding process of metadata into video begins. Data cannot be displayed until watermark process has completed. Implementations 2002 AFOSR Program Review

34. Sample Metadata and video footage XML Coded Metadata Surveillance Video 2002 AFOSR Program Review

35. Display Utility • JAVA based application that simplifies display of video & metadata • Abstracts user from separation of video & metadata 2002 AFOSR Program Review

36. Open Issues • Open problems in RVLC watermarking are • Capacity • Security • Channel bit errors • Non-burst errors • Forced invalidity 2002 AFOSR Program Review

37. T H E E N D 2002 AFOSR Program Review