Talk Slides

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© 2010 SALIENT STILLS INC.
Digital Media: The ins and outs
Jeff Hunter
CTO
Salient Stills Inc.
Digital Summit International 2010
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© 2010 SALIENT STILLS INC.
Contents
The important
concepts in a
digital media
file.
The computer’s
view of media
processing.
The problems
that can occur
processing
media and the
reasons why
they occur.
Digital Summit International 2010
A strategy for
dealing with
those
problems.
Tools and
resources that
we have found
useful in
dealing with
problem media
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© 2010 SALIENT STILLS INC.
Part I
The Nature of a Digital Media File
Digital Summit International 2010
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© 2010 SALIENT STILLS INC.
Digital Image Capture
176x144 image, 15 fps and
8KHz mono audio
Digital Summit International 2010
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© 2010 SALIENT STILLS INC.
The Capture Process
Digital Summit International 2010
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© 2010 SALIENT STILLS INC.
Turning it into Digital Sample
A raw video sample (typically one frame is one sample)
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and so on for a total of 76,032 bytes every 1/15
of a second
An raw audio sample (typically one second’s worth is one sample)
-50 -53 60 62 53 -73 -75 -70 -68 100 102 . . .
and so on for a total of 8000 bytes every second
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© 2010 SALIENT STILLS INC.
Recording the Samples
seconds
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5 minutes of video and audio is (76KB*15*300 + 8KB*300)
Digital Summit International 2010
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687MB
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© 2010 SALIENT STILLS INC.
Reducing the Video Sample Size
1001010100100
1010100101001
0010010010100
1001001001010
010000111111
One Raw Video Sample 76KB
Approximate the color
Approximate the motion
Video
Codec
Reduce the detail
Compact the data
One Compressed Video Sample 0.8KB
Digital Summit International 2010
1001
0101
0011
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© 2010 SALIENT STILLS INC.
Reducing the Audio Sample Size
10010101
00100101
01001010
One Raw Audio Sample 8KB
Approximate the
waveform
Remove
Audio
imperceptible sound
Codec
Compact the data
One Compressed Audio Sample 1.5KB
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011
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© 2010 SALIENT STILLS INC.
Recording the Samples
seconds
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5 minutes of video+audio is 3.6MB !
Digital Summit International 2010
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© 2010 SALIENT STILLS INC.
Keeping Track of Things
Media Header




Types of samples present (audio, video etc.)
Dimensions, durations of samples
The way samples are encoded (codec)
The location and timing of samples in the file
010100101010010101
010101010100101001
001010100100101010
101010100101010101
010110111010101101
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Digital Summit International 2010
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© 2010 SALIENT STILLS INC.
Creating the Digital File
201 190 167 184 157 139 101 98
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145 23
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190 180 177 206 222 197 240 …
-50 -53 60 62 53 -73 -75 -70 -68 100 102 . . .
• Record the video + audio signal
• Turn it into samples in memory
• Reduce the space each sample
takes up (compress)
• Record the (compressed)
samples to a disk file
• Record the “meta” information
in a header in the file
Digital Summit International 2010
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© 2010 SALIENT STILLS INC.
Summary
• Video In a Media File
– Recorded as a sequence of images taken at regular intervals (frames)
– The color of each pixel of the image are turned into numeric values
– All pixels values from one frame are collected together to form a video sample
• Audio In a Media File
– Audio is recorded as frequent a periodic measurement of the raw audio signal
– The measurement is turned into a numeric value (2 values for stereo etc)
– Measurements covering a specific period (e.g.. 1 second) forms a sample
• Media files contain
– A sequence of audio and video “samples” which may be ‘uncompressed’ but
most likely ‘compressed’ with codecs.
• Compression reduces data size to save on storage space or allow for transmission.
– A header which describes everything about the media samples
Digital Summit International 2010
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© 2010 SALIENT STILLS INC.
Part II
Formats, File Extensions
Digital Summit International 2010
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© 2010 SALIENT STILLS INC.
Proprietary -v- Non Proprietary
Formats
Location
of
Header
010100101010010101
010101010100101001
001010100100101010
101010100101010101
010110111010101101
010101010101011011
Organization of
samples from
different tracks
Type and structure of
information in header
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Choice of codec
and details of
encoding
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• Proprietary
– Organize in a non standard way perhaps to meet some functional or
business need
– Possibly use custom codecs
• Non Proprietary
– Organize according to a standard (e.g. avi, mov, mpg …).
– Use format supported codecs.
Digital Summit International 2010
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© 2010 SALIENT STILLS INC.
Non Proprietary Media Formats
• Public information available about the format
–
–
–
–
The specifics of how samples are organized
The specifics of the set of codecs supported
The specifics layout of the headers
etc. etc.
• Usually accompanied by
– Documents precisely explaining the above
• More importantly hopefully accompanied by
– Available processing libraries for others software vendors
to use
– Tools to encode and play the media on a variety of
platforms
Digital Summit International 2010
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© 2010 SALIENT STILLS INC.
No Guarantee Of Success
even for Non-Proprietary Formats
Wikipedia listed Standard
Container & Codec Formats
Over 20 Container Formats
(avi, mov, h264, mpg, flv …)
Over 50 Video Codecs
(dv, mp2, indeo, theora ..)
Over 90 Audio Codecs
(gsm, pcm, vorbis …)
That’s close to 100,000 different
possible media file configurations
Reduced because only certain codecs
associated with a specific container
format
Increased again because because of
the numbers of flavors of given
formats and codecs
Digital Summit International 2010
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© 2010 SALIENT STILLS INC.
File Extensions for Standard Formats
Provide the media file with a filename
with the appropriate extension
(e.g. 3gp, avi, mov, rm, mpg, vob, … )
myvideo.3gp
010100101010010101
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. . . the extension tells the OS and other
programs know what to expect for the
format.
Digital Summit International 2010
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© 2010 SALIENT STILLS INC.
Part III
Inside The Computer
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© 2010 SALIENT STILLS INC.
The Basic Windows Computer
WMA
WMV
AVI
WAV
AIFF
MPEG
MP3
AU
Windows
Media Player
YUV
JPG
AVI
RAW
....
Windows
Other
MPEG
DirectShow
MPEG4
....
Windows
Media
WMV
....
....
Digital Summit International 2010
File Associations
Applications
Media Libraries
Codecs
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© 2010 SALIENT STILLS INC.
Playing A Media File
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© 2010 SALIENT STILLS INC.
Double Click Application Launch
File association
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© 2010 SALIENT STILLS INC.
Processing the Format
Associated
library
YUV
JPG
Windows AVI
DV
H264
PCM AMR
Digital Summit International 2010
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© 2010 SALIENT STILLS INC.
Preparing to Play
H264
Windows AVI
dimensions .. ,
frame rate .. ,
durations …
encodings
video : JPEG,
audio : PCM
YUV
MP4
JPEG
Codec
instantiation
PCM
…. somewhere in the format header are the FOURCCs
which identify how the media samples (audio, video etc) are encoded.
Digital Summit International 2010
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© 2010 SALIENT STILLS INC.
Playing
Windows AVI
JPEG
PCM
decompressed audio
decompressed video
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© 2010 SALIENT STILLS INC.
The Components Used
WMA
WMV
AVI
WAV
AIFF
MPEG
MP3
Windows
Media Player
YUV
JPEG
AVI
Windows
RAW
PCM....
DirectShow
MPEG4
....
Windows
Media
WMV
....
....
QuickTime
Other
AMR
File Associations
Applications
Media
Frameworks
Codecs
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© 2010 SALIENT STILLS INC.
Adding QuickTime
WMA
WMV
AVI
WAV
AIFF
MPEG
Windows
Media Player
MP3
AU
GSM
3GP
AAC
DV
MOV
QuickTime Player
YUV
AVI
JPG
Windows
RAW
H264
....
QuickTime
DirectShow
MPEG4
....
Windows
Media
WMV
....
....
MPG4
DV
QuickTime
Other
File Associations
Applications
Media
Frameworks
Codecs
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© 2010 SALIENT STILLS INC.
Different Example – Our 3GP File
QuickTime
H264
AMR
decompressed audio
decompressed video
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© 2010 SALIENT STILLS INC.
File Open -v- Double Click
Double
Click
• OS decides on application
based on registered file
association
App. Open
File Open
• You decide on application
based on knowledge of
file and player capabilities
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© 2010 SALIENT STILLS INC.
Media Support in Other Applications
- making use of existing libraries
W
MA
W
MV
AVI
W
AV
AIF
F
MP
EG
Windows
Media Player
AVI
M
P3
AU
GS
M
3G
P
YU
V
JP
G
RA
W
DV
MOV
Forensic
Software
(for example)
QuickTime
Player
H2
64
....
QuickTime
DirectShow
AA
C
MP
G4
DV
MPE
G4
....
Windows WMV
Media ....
....
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© 2010 SALIENT STILLS INC.
The Process for this Case
User opens
application and
instructs application
to open file
QuickTime
Windows
DirectShow
AVI
JPE
G
Choose format from file
extension or user guidance
PC
PC
M
M
YES
Opens
successfully?
YES
Digital Summit International 2010
NO
More formats
available to
try?
NO
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© 2010 SALIENT STILLS INC.
Media Support in Certain Applications
- Replicating the Specifications
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MV
AVI
W
AV
AIF
F
MP
EG
Windows
Media Player
M
P3
AU
GS
M
3G
P
AA
C
DV
MO
V
VLC
(for example)
QuickTime
Player
H2
64
AVI
QuickTime
Support
YU
V
JP
G
RA
W
H2
64
....
QuickTime
DirectShow
MP
G4
DV
MPE
G4
AVI
Support
MP
G4
DV
MPEG
Support
YU
V
JP
G
RA
W
..etc
....
Windows WMV
Media
Support ....
Windows WMV
Media ....
....
Digital Summit International 2010
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© 2010 SALIENT STILLS INC.
Exporting & Conversion
User
User
Chooses
requests
the
codecs
exportfrom
as
User selects save
those
(for example)
available in
QuickTime
Forensic
Software
(for example)
H264
AVI
MPG4
QuickTime
DV
AMR
JPG
H264
PCM
AMR
decompressed video
decompressed video
Digital Summit International 2010
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© 2010 SALIENT STILLS INC.
Summary
• File extensions are principally
– a hint to the OS as to what application should started
– a hint to an application as to what the format is
• Media support is provided by software libraries that
– Process media conforming to a particular format(s)
– Have an associated set of codec’s to deal with the samples
in the media
• Media processing applications may
– Be able to make use of one or more of these libraries and
associated codecs
– Provide their own versions of everything
Digital Summit International 2010
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© 2010 SALIENT STILLS INC.
Part IV
What could possibly go wrong?
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© 2010 SALIENT STILLS INC.
Plenty ..
Digital Summit International 2010
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© 2010 SALIENT STILLS INC.
It’s an .AVI file but it doesn’t play!
Windows AVI
JPEG
LRX
PCM
• Not a regular AVI file
• Uses a codec which is not in the AVI suite
• Not encoded in the way the codec expects
Digital Summit International 2010
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© 2010 SALIENT STILLS INC.
Expanding on that ...
• Not a regular AVI file
– It is technically an AVI file but it is a structure that is proprietary
(e.g. has extra tracks that the player does not expect).
• It contains media samples that are encoded with a codec
that is not available
– The codec was available on the system that created it
• The stated encoding of the media sample is not how it is
encoded
– Sample does not conform to the ‘AVI version’ of that encoding
– Its some other proprietary encoding that has been given the
same name (four cc)
• Often true of files exported from DVR system or DVR player
applications.
Digital Summit International 2010
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© 2010 SALIENT STILLS INC.
Proprietary DVR Software
• DVR media file format structure is nearly always
proprietary
– Designed to contain extra information pertaining to
the security system etc.
• DVR software may make use of parts of the
common media libraries e.g. AVI, DirectShow
– Samples in file may be encoded using standard codecs
– May install codecs and/or use codec services.
– May use file writing support for export.
Digital Summit International 2010
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© 2010 SALIENT STILLS INC.
Proprietary DVR Software
W
MA
W
MV
AVI
W
AV
AIF
F
MP
EG
Windows
Media Player
AVI
M
P3
AU
GS
M
3G
P
DV
MO
V
Forensic
Software
(for example)
QuickTime
Player
DSF NDX
REM
Rapid
Eye
Loronix
PelcoPlayer
Player
Player
Media
dsfProcessing
format
Media Processing
Library
Processing
Library Library
r
e
m
4
D
V
YU
VLRX
JP
G
RA
W
H2
64
....
QuickTime
DirectShow
AA
C
MP
G4
DV
MPE
G4
....
Windows WMV
Media ....
....
Digital Summit International 2010
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© 2010 SALIENT STILLS INC.
It’s and MPEG file and it doesn’t play
• MPEG has more than one standard (all possibilities in
security media context)
– MPEG1 (originally used to fit video data onto CD’s)
– MPEG2 (used for encoding of video on DVD (vob) files, also for
digital cable and satellite TV)
– MPEG4 (used in Blue-Ray and for web video etc)
• MPEG standards have many parts, profiles and levels.
– Profiles define support for features like types of compression,
color formats etc
– Levels define support for specific values like frame rates,
resolution etc.
– Different parts in MPEG4 offer more advanced concepts (3D
scene support, Advanced encoding e.g. H264 etc)
Digital Summit International 2010
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© 2010 SALIENT STILLS INC.
Many MPEG Flavors
Container Format
Company
Video Codecs
Audio Codecs
3GPP
H.263, MPEG-4 Part 2 and H.264/MPEG-4 AVC
AMR-NB/WB, AMR-WB+and (HE)-AAC
Advanced Systems Format(.asf, .wma,
.wmv)
Microsoft
Almost anything through VFW or
DMO; H.264/AVC is problematic
Almost anything throughACM or DMO;
AVI
Microsoft
Almost anything through VFW;H.264/AVC is
Almost anything through ACM;
problematic due to the limited B-frame support[
DivX Media Format(.divx)
DivX, Inc.
MPEG-4 Part 2 video encoded to meet DivX
profiles
MP3, PCM, AC-3
MPEG
MPEG-2 Part 2,H.264/MPEG-4 AVC, VC-1
AC-3, E-AC-3, Dolby TrueHD, Linear
PCM, DTS,DTS-HD, MPEG-2 Part 3
Adobe Systems
Sorenson, VP6, Screen Video,H.264/MPEG-4
AVC[
MP3, Nellymoser, ADPCM, raw PCM, AAC[
MP4
MPEG
MPEG-1, MPEG-2, H.263, MPEG-4 ASP, VC1/WMV, H.264/MPEG-4 AVC
MPEG-1 Layers I, II, III (MP3), MPEG-2/4 (HE)AAC, AC-3, Vorbis, Apple Lossless
MPEG Video File (.mpg, .mpeg)
MPEG
MPEG-1, MPEG-2
MPEG-1 Layers I, II, III (mp3), LPCM
MPEG-2 PS Program Stream(.ps)
MPEG
MPEG-1, MPEG-2
MPEG-1 Layers I, II, III (mp3), AC-3, LPCM, DTS
MPEG-2 TS Transport Stream(.ts)
MPEG
MPEG-1, MPEG-2, MPEG-4 ASP, H.264, VC-1
MPEG-1 Layers I, II, III (mp3), AC3, LPCM, DTS,AAC
MPlayer team/NUT Project
Virtually anything
Virtually anything
Xiph.org
Theora, almost anything through VFW
Limited to what is available to
theQuickTime codec manager
Vorbis, almost anything through ACM
Limited to what is available to Sound
Manager or Core Audio
(HE)-AAC, Cook Codec,Vorbis, RealAudio
Lossless
AC-3, Linear PCM, DTS, MPEG-2 Part 3, MPEG-1
Layer II
3GP
EVO
Flash Video(.flv)
NUT
Ogg / OGM
QuickTime (.mov, .qt)
RMVB
VOB+IFO
Apple
RealNetworks
RealVideo 8, 9, 10
DVD Forum
MPEG-2 Part 2
…..
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It’s and MPEG file and it doesn’t play
• Lack of native support on Windows
– For MPEG-2
• Microsoft OS libraries require plug-ins or codec packs.
• QuickTime requires the QuickTime add-on
– For MPEG-4
• Microsoft OS only provides the codec but does not support the
file format.
• Microsoft has proprietary MPEG4 encodings (Microsoft v1,v2,v3).
• QuickTime 7 required for H264 support (MPEG part 10)
• No full implementations of standards
– Codec packs and plug-ins generally provide only a small
subsets of profiles, or parts.
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Adding MPEG Support
W
MA
W
MV
AVI
W
AV
AIF
F
MP
EG
Windows
Media Player
AVI
M
P3
AU
GS
M
3G
P
AA
C
H2
64
....
MPEG2
MPG
MPE
DirectShow G4
MO
V
Forensic
Software
(for example)
QuickTime
Player
YU
V
JP
G
RA
W
DV
QuickTime
MP
G4
DV
....
MPEG1
Windows WMV
Media ....
....
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The media plays in WMP but my
forensic software ..
Loads it but then slows down or crashes
• Temporally Compressed Media
– samples probably use a codec where decompressing one
sample to produce a frame depends on decompressing
many other samples first (e.g. mpeg, wmv …)
• Streaming Media
– there may no information in the header as to where each
sample is – they just have to be read in order – (like a
book with no table of contents).
OK for players
Bad for applications that want to
access frames in random order
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Summary
• The following problems are common with ‘standard
format’ files produced from DVRs
– Files with non-compliant format
– Media samples encoded with missing codecs
– Media samples with non-compliant encoding
• MPEG is not well supported without addition to the
OS
• Formats designed for streaming don’t perform well
‘as is’ in forensics applications
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Part V
What to do about it.
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Does the media seem
to be in a standard
format ? e.g. mov, avi,
wmv, mpg etc ?
Solution Approach
YES
NO
Does the media import
and review in your
forensic software?
Export
from player
Can a proprietary
player be used to
export to a standard
format?
NO
YES
Install codec
NO
YES
Does the media
load and play in any
conversion utility?
YES
NO
Does the media
play in any player?
NO
YES
YES
Screen Capture
Capture the playing media from
the proprietary player window
using your forensic software
Does the media
contain a proprietary
codec that has not
been installed?
NO
YES
Does the media
play in any
player?
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NO
Done
No action
needed
Conversion
Convert to a standard
format and codec
using conversion
software
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Does the media
import and review in
your forensic
software?
• Your forensic software may well import the video ..
in particular it may offer
Conversion
– OS based multi format and codec support.
– trans-coding approaches to deal
with streaming formats.
– screen capture facilities for
proprietary player import
• However ..
Convert to a standard
format and codec
using conversion
software
Screen Capture
Capture the playing media
from the proprietary player
window using your forensic
software
– Even if formats and codecs are installed it may fail
– Forensic video vendors cannot focus exclusively on
developing media support so other tools are
useful/necessary
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Does the media load
and play in any
conversion utility?
• Conversion utilities can be powerful
– developers focus specifically on media playing and converting
– commercially untenable effort is put into some of them
•
Developer quote “Proof that I had too much free time in college”
• Worthwhile trying more than one utility
– tools often have specific strengths in particular media formats
• When converting be sure not to degrade quality
– Look for output options that use no compression .. often
described as raw.
– Verify that output is indeed uncompressed .. look for “raw” or
“none” as media sample encoding
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Does the media
contain a proprietary
codec that has not
been installed?
This a difficult question
• Two pieces of knowledge required
A. What codecs are used in the media?
B. What codecs do I have installed that are available
when processing this format?
Tools can help
But keep a healthy degree of skepticism
• Not always 100% accurate
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Can a proprietary
player be used to
export to a standard
format?
• Finding a player can be challenging
– Resources like Media-Geek or manufactures web site
are good place to start
• Exporting is not always available
– If it is a security DVR media player it is an uncommon
option
• Avoid further degradation
– Security DVR player may recompress on export
• Screen capture may be the better option anyway
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Screen Capture
Capture the playing media
from the proprietary player
window using your forensic
software
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Summary
• Use tools on the problem media to get it to open
properly
–
–
–
–
Your forensic video software
Format conversion tools
Codec investigation tools
Codec packs
• Beware of quality degradation on any conversion
or export
– Choose ‘raw’ sample encoding if possible
• If all fails then find something that will play it and
screen capture
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Part VI
Where to look for help
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Resources
•
•
•
QuickTime Pro
MOV and MPEG file conversion
http://www.apple.com/quicktime/pro/
– useful for format conversion of QuickTime files but with MPEG add-on can be
helpful dealing with mpeg .vob files
Virtual Dub
AVI file conversion
http://www.virtualdub.org/
– Reliable conversion of most avi files including files with installed proprietary
codecs
ASF Convertor
ASF file conversion
http://www.boilsoft.com/asfconverter/
– Handles cases where other software has not been able to play windows media
files
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Resources
•
MediaInfo
Container and Codec determination
http://sourceforge.net/projects/mediainfo/
•
•
•
– Alternative to GSpot, promising reviews
GSpot
Codec determination
http://www.headbands.com/gspot/
– Helpful in determining the specific codec present in a media file
Installed Codec
Review , disable/enable installed codecs
http://www.nirsoft.net/utils/installed_codec.html
– Helpful if a “rogue” codec is causing instabilities in the rest of the system
DivX
Codec set and tools
http://www.divx.com/
– Useful additional install to improve support for mpeg related formats
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Resources
•
•
VLC
Player for a wide number of formats
http://www.videolan.org/vlc/
– Useful for viewing media of a wide variety of standard formats and codecs
MPEG StreamClip
Player for MPEG formats
http://www.squared5.com/svideo/mpeg-streamclip-win.html
•
•
– Useful for viewing media and describing encoding
DVDCheck
Display compatibility of MPEG2 decoders
http://www.google.com/search?query=Microsoft%20DVDCheck
– Lists installed MPEG2 support and compatibility with Windows media player
Microsoft Article
Format support on Windows
http://support.microsoft.com/kb/316992
– Describes what is supported by default on Windows and playable in WMP.
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Resources
Media Geek
http://media-geek.com/
• Administered and operated by Larry Compton
• Site for “The Forensic Multimedia Community”
– Source of players for proprietary file formats
– Source of codecs for formats containing proprietary codecs
– Many other tools, documents and other resources pertaining to
forensic media.
• Restricted membership for government employees and
related persons in the forensic community
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Contact Information
[email protected]
617 987 8200 x 205
www.salientstills.com
(news->events->tradeshows)
Digital Summit International 2010