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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. Outline. Data hiding/watermarking requirements

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Afosr program review data hiding in compresed digital video

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


Outline
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


Background
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


Data hiding requirements
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


State of video watermarking
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


The medium
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


Distinction with a difference
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


Mpeg bitstream syntax
MPEG bitstream syntax

2002 AFOSR Program Review



Label carrying vlcs
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


Data hiding in lc vlc
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


Data hiding capacities data
Data hiding capacities:data

2002 AFOSR Program Review


Lossless video watermarking using error resilient vlcs

Lossless video watermarking using error-resilient VLCs*

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


The idea watermark as intentional bit errors
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


The solution lossless watermarking
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


Two way decodable vlcs
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


Code structure
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


Watermarking using bidirectional codes
Watermarking using bidirectional codes

VLCs:

Message:{a,b,d,c}

Bidirectional VLC

Watermarked w={w1,w2,w3,w4) bidirectional VLC

2002 AFOSR Program Review


Watermark detection
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


Distance properties
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


Watermarking capacity
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


Implementation
Implementation

2002 AFOSR Program Review


Self watermarking

SELF-WATERMARKING*

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


Self watermarking the concept
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


Self watermarking of compressed video
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


Watermark extraction
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


Watermark embedding
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


Data

2002 AFOSR Program Review


Watermarking capacity1
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



Background1
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


Metadata watermarking
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


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.

Implementations

2002 AFOSR Program Review


Sample metadata and video footage
Sample Metadata and video footage

XML Coded Metadata

Surveillance Video

2002 AFOSR Program Review


Display utility
Display Utility

  • JAVA based application that simplifies display of video & metadata

  • Abstracts user from separation of video & metadata

2002 AFOSR Program Review


Open issues
Open Issues

  • Open problems in RVLC watermarking are

    • Capacity

    • Security

    • Channel bit errors

    • Non-burst errors

    • Forced invalidity

2002 AFOSR Program Review


T H E E N D

2002 AFOSR Program Review


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