1. AFOSR PROGRAM REVIEW DATA 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. 2002 AFOSR Program Review 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

3. 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

4. 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

5. 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

6. 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

7. 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.

8. 2002 AFOSR Program Review 8 MPEG bitstream syntax

9. DATA HIDING IN VLCs

10. 2002 AFOSR Program Review 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

11. 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

12. 2002 AFOSR Program Review 12 Data hiding capacities:data

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

14. 2002 AFOSR Program 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.

15. 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

16. 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)

17. 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

18. 2002 AFOSR Program Review 18 Watermarking using bidirectional codes VLCs:Message:{a,b,d,c} Bidirectional VLC Watermarked w={w 1,w 2,w 3,w 4 ) bidirectional VLC

19. 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}

20. 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  min bits.

21. 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

22. 2002 AFOSR Program Review 22 Implementation Video VLC Statistics # of frames # of slicesAvg# of slices/fr Avg# of VLC/slice Capacity (bits) Video#187178399178133,263 Video#28466 1550143,922 Video#3396 130516,732

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

24. 2002 AFOSR Program Review 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

25. 2002 AFOSR Program Review 25 Self-watermarking of compressed video 10 VLC (0,5) VLC (0,16) VLC (1,15) VLC (0,6) VLC (1,10) VLC (1,11) VLC (0,12)

26. 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

27. 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

28. 2002 AFOSR Program Review 28 Data StreamFile SizeFrame Size (MB) Frame Types MPEG1892kB24x1613I,78B,65 P MPEG22257kB45x363I,8P,20B Frame SizeGOP 1 LCVLC # GOP 2 LCVLC # GOP 3 LCVLC # 372x246299730083061 720x576326801127914463

29. 2002 AFOSR Program Review 29 StreamAverage Capacity (bits/frame) MPEG1I = 2958, P = 13, B = 0 MPEG2I = 18125, P = 501, B = 2 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.

30. Metadata Embedding

31. 2002 AFOSR Program Review 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

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

33. 2002 AFOSR Program Review 33 Implementations 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.

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

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

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

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