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AFOSR PROGRAM REVIEW DATA HIDING IN COMPRESED DIGITAL VIDEO

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Title: 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

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
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
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
The medium
  • Understanding the medium is a prerequisite to
    watermarking it
  • Uncompressed NTSC video runs at 168 Mb/sec.
    MPEG-2 runs at lt10 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
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
MPEG bitstream syntax
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
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
Data hiding capacitiesdata
13
Lossless video watermarking using error-resilient
VLCs
  • B. Mobasseri, Watermarking of Compressed
    Multimedia using Error-Resilient VLCs, MMSP02-
    in review

14
The ideawatermark 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
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
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

vlcfliplr(vlc)
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
Watermarking using bidirectional codes
VLCs
Messagea,b,d,c
Bidirectional VLC
Watermarked ww1,w2,w3,w4) bidirectional VLC
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
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
Watermarking capacity
  • Watermarking capacity of a VLC falls under two
    categories
  • Ll, in this case
  • CL bits/packet
  • Lgtl, watermark burst may cross over to the L-l
    bits of the next VLC. It follows that

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

24
Self-watermarkingthe 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
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
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
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
Data
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.

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
32
Metadata Watermarking
Video Buffer
MPEG Encoder
Display
Watermarked Video
W
Metadata Buffer
Store
Watermarking system combines both video and
metadata feeds to form a single, less cumbersome
stream that can be both displayed and stored.
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
Sample Metadata and video footage
Surveillance Video
XML Coded Metadata
35
Display Utility
  • JAVA based application that simplifies display of
    video metadata
  • Abstracts user from separation of video
    metadata

36
Open Issues
  • Open problems in RVLC watermarking are
  • Capacity
  • Security
  • Channel bit errors
  • Non-burst errors
  • Forced invalidity

37
T H E E N D
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