AFOSR PROGRAM REVIEW DATA HIDING IN COMPRESED DIGITAL VIDEO

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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

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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

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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

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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

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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

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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

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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.

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MPEG bitstream syntax
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DATA HIDING IN VLCs
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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
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Data hiding in lc-VLC

• The algorithm proposed by Langelaar embeds
  watermark bits in the LSB of the level of the
  lc-VLCs

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Data hiding capacitiesdata
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Lossless video watermarking using error-resilient
VLCs

• B. Mobasseri, Watermarking of Compressed
  Multimedia using Error-Resilient VLCs, MMSP02-
  in review

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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.

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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

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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)
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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

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Watermarking using bidirectional codes
VLCs
Messagea,b,d,c
Bidirectional VLC
Watermarked ww1,w2,w3,w4) bidirectional VLC
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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

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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.

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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

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Implementation
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SELF-WATERMARKING

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

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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

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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
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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

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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

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Data
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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.

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Metadata Embedding
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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
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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.
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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.

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Sample Metadata and video footage
Surveillance Video
XML Coded Metadata
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Display Utility

• JAVA based application that simplifies display of
  video metadata
• Abstracts user from separation of video
  metadata

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Open Issues

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

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T H E E N D