DVCAMformat

transcript

8/9/2019 DVCAMformat

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THE DVCAM FORMATTHE DVCAM FORMAT

Clyde CunninghamClyde Cunningham

Copyright 2005 Clyde Cunningham


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The Sony DVCAM format is based on theInternational Electrotechnical Commission

DV standard

IEC 61834IEC 61834

This document consists of ten parts, of which only Parts 1 and 2

are related to standard definition video recording.

The remaining parts define the format for HDTV, EDTV, DVB

and DTV applications.


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BASIC DVCAM PARAMETERSBASIC DVCAM PARAMETERS


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Track pitch 15m

Track angle 9.1752

Tape speed 28.247mm/s

Tape width 6.35mm

Drum diameter 21.7mm

Track azimuth -20/+20

Tape type Metal evaporated

MechanicalMechanical


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ElectricalElectrical

Bit rate to tape 41.85 Mb/s

Video bit rate 24.948 Mb/s

Minimum wavelength 0.49m

Modulation SNRZI PRIV(24 to 25 bit)

Error correction Reed-Solomon

Cross interleaved

Tracks per TV frame 625/50 12525/60 10


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Lines recorded 625/50 23 - 310335 - 622

525/60 23 - 262

285 - 524

Sampling structure 625/50 4:2:0

525/60 4:1:1

Compression Intra-frame DCT

Adaptive quantizationModified 2-D Huffman

VideoVideo


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AudioAudio

2 Channel mode 16 bit linear/48kHz

4 Channel mode 12 bit non-linear/32kHz

In the DVCAM standard

the audio sampling rate

MUST be lockedto video frame rate


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A DVCAM recording where theaudio sampling rate is not locked

to video frame rate is considered

to be NON-STANDARD.

This will be indicated on the front

panel of DVCAM units as

NS or Not editable


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DVCAM VIDEO PROCESSINGDVCAM VIDEO PROCESSING


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4:2:2 Video Sampling4:2:2 Video Sampling

A n a l o gt o

D i g i t a lC o n v e r t e r

Y

1 3 . 5 M H z ( 4 )

A n a l o gt o


C b ( B - Y )

6 . 7 5 M H z ( 2 )

A n a l o gt o


C r ( R - Y )

6 . 7 5 M H z ( 2 )

8 b i t s

8 b i t s

8 b i t s

A N A L O G 4 : 2 : 2 D I G I T A L


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4:2:2 Sampling Structure4:2:2 Sampling Structure


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Colour Sample DecimationColour Sample Decimation

D e l a y

D e c i m a t i o nF i l t e r


I N P U T4 : 2 : 2

O U T P U T4 : 1 : 1 ( 5 2 5 / 6 04 : 2 : 0 ( 6 2 5 / 5 0

Y

C b

C r


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Why is filtering necessary?

Why cant you just throw away

every alternate colour sample?


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6 . 7 5 M h z 1 3 . 5 M h z 2 0 . 2 5 M h z3 . 3 7 5 M h z

S A M P L E D C O L O U R - D I F F E R E N C E S P E C T R U

4:2:2

6 . 7 5 M h z 1 3 . 5 M h z 2 0 . 2 5 M h z3 . 3 7 5 M h z

S A M P L E D E C I M A T I O N W I T H O U T F I L T E R I N G

A L A I S I N GA L A I S I N GA L A I S I N GA L A I S I N GA L A I S I N GA L A I S I N G

1 0 . 1 2 5 M h z 1 6 . 8 7 5 M h z

4:1:1

6 . 7 5 M h z 1 3 . 5 M h z 2 0 . 2 5 M h z1 . 6 8 7 5 M h z

F I L T E R E D C O L O U R - D I F F E R E N C E S P E C T R U M ( b

4:2:2

4:1:1

F I L T E R E D C O L O U R - D I F F E R E N C E S P E C T R U M (

6 . 7 5 M h z 1 3 . 5 M h z 2 0 . 2 5 M h z3 . 3 7 5 M h z 1 0 . 1 2 5 M h z 1 6 . 8 7 5 M h z


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4:1:1 colour samples decimated HORIZONTALLY.

So Horizontal filtering is necessary.

4:2:0 colour samples decimated VERTICALLY.

So vertical filtering is necessary.


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4:2:0 Video Sampling Structure4:2:0 Video Sampling Structure


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4:1:1 4:2:04:1:1 4:2:0

Colour Resolution ComparisonColour Resolution Comparison


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Effect of Sample Decimation on Colour ResolutionEffect of Sample Decimation on Colour Resolution

1 . 5 M H z

H o r i z o n t a l c o l o u r r e s o l u t i o n

( = 1 2 0 L i n e s r e s o l u t i o n )3 M H z

4 : 2 : 2

( = 2 4 0 L i n e s r e s o l u t i o n )

4 : 1 : 1

2 0 0 L i n e s

V e r t i c a l c o l o u r r e s o l u t i o n

4 0 0 L i n e s

4 : 2 : 2 4 : 2 : 0


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4:1:1 Horizontal colour resolution = 120 Lines

4:1:1 Vertical colour resolution = 400 Lines

4:2:0 Horizontal colour resolution = 240 Lines

4:2:0 Vertical colour resolution = 200 Lines

SummarySummary


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Tape FormatTape Format


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DVCAM Basic Drum ConfigurationDVCAM Basic Drum Configuration

D R U M

1 R e v o l u t i o n = 2 T r a c

D r u m S p e e d = 9 0 0 0 r p m


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DVCAM Track FootprintDVCAM Track Footprint

ITI: Insert Tracking Information

A u di o

ITI

V ide o

S u bc o d

e

D ir ec tio

n ofh e a

d mo tio

n

D i r e c t i o n o f t a p e t


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DVCAM RF WaveformDVCAM RF Waveform


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TrackingTracking

The data stream recorded on the tape is encodedusing a technique called 24 to 25 bit modulation.

An extra bit is added to the beginning of everythree randomized (scrambled) bytes.

The value of the extra bit is chosen to shape the

frequency spectrum after NRZI encoding.


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Each track is one of the following types -Each track is one of the following types -

F0F0 F1F1 F2F2


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F r e q u e n c y ( M H z )

L e v e l( d B )

F 1 F 2

F0 TrackF0 Track

F1: Bit rate/90 (465 kHz)

F2: Bit rate/60 (697.5 kHz)

Recorded spectrumRecorded spectrum


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F1 TrackF1 Track




L e v e l( d B )

F 1 F 2



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F2 TrackF2 Track




L e v e l( d B )

F 1 F 2



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Tracking Frequency SequenceTracking Frequency Sequence

F 0 F 1 F 2 F 1F 0 F 0 F 0 F 0 F 0F 1F 2 F 2


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TrackingTracking Signal ProcessingSignal Processing

4 6 5 k H zD e t e c t

6 9 7 . 5 k H zD e t e c t

P l a y b a c k R F

F 0 F 1 F 0 F 2 F 0F 1

F 2

T r a c k i n g S i g n a l

Note that only one head reads the tracking signals.


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During normal playback, the servo system uses

the tracking signals from the entire track..

During insert editing, the servo system uses

only the ITI sector.


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Recorded Data StructureRecorded Data Structure


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Audio and video data is written to the tape in packets called -

Sync BlocksSync Blocks

Each Sync Block contains -

2 Synchronizing bytes

3 Sync Block identification bytes

77 bytes of data (the payload)

8 bytes of Reed-Solomon Inner Error Correction codes

Total number of bytes in a Sync Block = 90


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Sync Block StructureSync Block Structure

One Sync Block = 0.2mm (approx)

0 4 5 8 1 8 98 2

B y t e N u m b e r 1 2 3

D a t a b y t e sI n n e r E r r o r C o r r e c t i o n C o d e sI D ( S y n c B l o c k i d e n t i f i c a t i o n )S y n c ( S y n c h r o n i z i n g b y t e s )

7 7 b y t e s 8 b y t e s


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Audio Product BlockAudio Product Block

A u d i o D a t a

A u d i oA u x i l i a r y

D a t a

I n n e r R e e d -S o l o m o n

C o d e s

O u t e r R e e d -

S o l o m o nC o d e s

0 4 5 9 8 1B y t e N u m b e r

1 0 8 2 8 9

1

4

D

a

ta

S

y

n

c

-b

lo

c

k

s

I DS

y

n

c


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Video Product BlockVideo Product Block

S T R U C T U R E O F T H E S Y N C - B L O C K S I N

V i d e o D a t a

I n n e r R e e d -S o l o m o n

C o d e s

O u t e r

R e e d -S o l o m o n

C o d e s

S

y

n

c

0 4 5 9 8 1B y t e N u m b e r 1 0 8 2 8 9

1

4

9

D

a

ta

S

y

n

c-

b

lo

c

k

s

V i d e o A u x i l i a r y D a t a

V i d e o a u x i l i a r y d a t a

I D


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Video Data Rate ReductionVideo Data Rate Reduction

8-bit serial data rate 216 Mb/s

Colour resolution halved 162 Mb/s

H and V blanking removed 125 Mb/s

DV target data rate 25 Mb/s

Compression ratio 5:1


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Video Data RateVideo Data RateReduction ProcessesReduction Processes


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First StageFirst Stage

ofof

Video CompressionVideo Compression

BlockingBlocking

Blocking is the partitioning of the Y, Cb and Cr

samples of the TV frame into 8x8 pixel blocks.


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6480 Y blocks6480 Y blocks

1620 Cb blocks1620 Cb blocks

1620 Cr blocks1620 Cr blocks

414720 Y pixels414720 Y pixels

103680 Cb pixels103680 Cb pixels

103680 Cr pixels103680 Cr pixels


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Each Y, Cb and Cr pixel block is then subjected to a mathematical

process called a Discrete Cosine Transform (DCT).

DCT transforms the 8x8 pixel blocks from time-domain

information into space-frequency domain information.

The purpose of this is to make use of the statistical nature of TV

images to reduce the amount of data representing the picture.


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DCT

(DCT: Discrete Cosine Transform)

Time DomainTime Domain

8x8 pixel blocks

Space-frequency DomainSpace-frequency Domain

8x8 coefficient blocks


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The Basis Pictures are all unique - no two make up a third.

The numbers in the space-frequency block represent the

DCT coefficients (or proportions) of 64 Basis Pictures.

Basis Pictures


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DCT Basis PicturesDCT Basis Pictures

AC coefficients

DC coefficient Increasing horizontal detail

I

ncrea

sing

verticaldetail


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Typical DCT Coefficients For One DCT BlockTypical DCT Coefficients For One DCT Block

Note that the low frequency coefficients have the largest values and

the high frequency coefficients have the lowest values.

Statistically this is the most common situation in a TV image.

Note also that whereas all the time domain values are finite


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Note also that, whereas all the time-domain values are finite,

many of the DCT coefficient values are zero.

However, some of the DCT coefficient values will be large because

the sum of the squares (power) of the time-domain values equals

the sum of the squares of the space-frequency domain values.

In other words, the picture appears to be more efficiently

represented by DCT coefficients than by time-domain values.


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If the image to be compressed is a colour bar test waveform, then almost all the DCT

coefficients will be zero.

Using an 8x8 area of the green bar as an example, note that there is no horizontal

detail and no vertical detail. So the DCT Block will have the following values -

1 4 9 0

0

0

0

0

0

0

0

0

0

0

000

0

0

0 0

0 0 0 0

0

0 0

0

0 0

0 0

0

0

0 0

0 0

0 0

0 0 0

0 0 0 0

0 0 0 0

0 0 0 0

0 0 0 0

0 0

0 0

0

0

The indicated area of the colour bar is represented by one finite number only.


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But there is a problem!But there is a problem!

When there is horizontal movement between the fields

in a frame, large vertical detail can be generated.

No movement between fields Movement between fields

Vertical detailVertical detail

F1F1 F2F2

Large vertical high-frequency DCT coefficients are generated

if the image moves horizontallly.


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When significant movement is detected between the fields,When significant movement is detected between the fields,

each 8x8 pixel block is broken into two 8x4 blocks as follows -each 8x8 pixel block is broken into two 8x4 blocks as follows -

The DCT transformation is then performed over the entire

modified 8x8 pixel block.

AA

CC

EE

GG

BB

DD

FF

HH

Original 8x8 pixel block

A+BA+B

C+DC+D

E+FE+F

G+HG+H

A-BA-B

C-DC-D

E-FE-F

G-HG-H

Modified 8x8 pixel block


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When there is no movement between the fields the processing

mode is called -

8x8 DCT Mode

When there is significant movement between the fields the

processing mode is called -

2-4-8 DCT Mode

This information is transmitted with the coefficient data so that

the pixel values can be reconstructed correctly in the decoder.


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Up to this pointUp to this point

all the processes areall the processes arecompletely reversible.completely reversible.


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QuantizationQuantization

(scaling the coefficients)

This is NOT completely reversible.

Causes compression artefacts.


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Quantization is the scaling of the AC coefficients in the DCT Blocks.

Quantization is done using a Quantization Table, which is chosen

according to the absolute magnitude of the largest AC coefficient

and the visibility of the errors after quantization has been

performed.

There are 16 Quantization Tables in the DV format.

This is done to reduce the values of the coefficients, because

lower values (most probable) are transmitted with a small number

of bits and higher values (least probable) are transmitted with a

larger number of bits (called Variable Length Coding). So reducing

the values of the coefficients reduces the total number of bits

representing the data in the DCT block


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The numbers inbluecome from the quantization table for this DCT block.

Note that the DC coefficient is not quantized.

Also note that the quantization steps for the high spacial-

frequency components are larger than than the steps for low

spacial-frequency components


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Quantized Coefficients

Note that the values are truncated (e.g. 37/2 = 18)


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At the decoder the quantized coefficients in each DCT block are

multiplied by the same quantization steps as used in the encoder.

Because of truncation, some re-quantized coefficients will have errors.

The high frequency coefficients have the greatest errors because the

quantization steps are more severe for high frequency coefficients

than for low frequency coefficients.

Compression artefacts (or mosquitos) are the result of these errors.


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Original Coefficient Values Re-quantized Coefficient Values

The numbers in red indicate which of the re-quantized

coefficients have errors.


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Zig-Zag ScanZig-Zag Scan


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Advantage can be taken of the large number of zeros in thequantized DCT coefficient block.

By scanning the block in a zig-zag pattern the sequence ofzero coefficients can be encoded more efficiently.

This is called Run-Length encoding.


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1 2 0 8 3 5 9 1 8 0

0

0

0

0

0

0

0

0

0

0

0

0

0

000

0

0

0 0

0 0 0 0

0

0 0

6 2 0

7 59 7 - 2 1 1 1 3

- 2

2 0

0

0

1

3

1 1

4 3 1 5 8 7

5

3 - 1

4

2

2

1 0

1

0

0

0

Zig-Zag ScanZig-Zag Scan

120, 83, 97, 43, 75, 59, 18, -21, 15, 11, 3, 5, 8, 11, 6, 2, 3, 7, 4, 3, 1, 0, 1, 2, 2,

-2, 2, 0, 0, 0, 0, 1, -1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,

0, 0, 0, 0, 0, 0, 0, 0


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In the DV system, the binary code word representing a run is

determined by the number of repeated zero coefficients and the

absolute amplitude of the coefficient immediately following therun.

Statistically the amplitude of a coefficient at the end of a run is

more likely to be small rather than large so the length of the binary

code words representing the runs are chosen to have fewer bitsfor small amplitudes and more bits for large amplitudes.

This is called Modified 2-D Huffman coding.


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120, 83, 97, 43, 75, 59, 18, -21, 15, 11, 3, 5, 8, 11, 6, 2, 3, 7, 4, 3, 1,

0, 1,

2, 2, -2, 2,

0, 0, 0, 0, 1,-1,

0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,

0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,

0, 0, 0

In the previous case the 64 DCT coefficients are reduced to 31

codewords.

The numbers in red are represented by one binary code word only.


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Macro Blocks, Video SegmentsMacro Blocks, Video Segments

andandSuper BlocksSuper Blocks


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Because there is limited data-space on the tape, it is necessary to

make sure that the space is used efficiently.

Some areas of the TV frame will have few high frequency

components so the DCT blocks representing those areas will have

few finite AC coefficients.

If each DCT block was allocated a fixed number of bytes on the

tape then much of the data-space would be wasted.

The following techniques are used to make sure that the space is

used as efficiently as possible -


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Macro BlockingMacro Blocking

One Macro Block = Four Y DCT Blocks+ One Cb DCT Block

+ One Cr DCT Block

(6480 Macro Blocks = one TV Frame)

Y

C rC b

6 2 5 / 5 0 M a c r o B l o c k

Vid S tVideo Segment


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Video SegmentVideo Segment

TV FrameTV Frame

One Video Segment = Five pseudo-randomly selected Macro Blocks

(1296 Video Segments/TV Frame)


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One Video Segment

is compressed into

5 x 77 = 385 bytes = 3080 bits

77 bytes = One Compressed Macro Block

= the data payload of a Video Sync Block

7 7 b y t e s7 7 b y t e s7 7 b y t e s7 7 b y t e s7 7 b y t e s

Excess data from one Compressed Macro Block

is passed to vacant spaces in other blocks

within the same video segment.

S Bl kSuper Blocks


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Super BlocksSuper Blocks

Numbers indicate the order of transmission

C o m p r e s s e d M a c r o B l o c k

0

1

2 3

4

5 6

7

8 9

1 0

1 1 1 2

1 3

1 4 1 5

1 6

1 7 1 8

1 9

2 0 2 1

2 2

2 3 2 4

2 5

2 6

T V F r a m e

One Super Block = 27 Compressed Macro Blocks

T k Di t ib ti f S Bl kT k Di t ib ti f S Bl k


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Track Distribution of Super BlocksTrack Distribution of Super Blocks

S u p e r B l o c k ( 0 , 0 )

T r a c kN u m b e r

1

0

2

3

4

5

6

7

8

9

1 0

1 1

B o t t o m e d g e o f t h e t a p e T o p e d g e o f t h e t a p e

O

rd

e

r

o

f

R

e

c

o

rd

in

g

D i r e c t i o n o f H e a d M o t i o n

S u p e r B l o c k ( 0 , 1 )

S u p e r B l o c k ( 1 , 0 )S u p e r B l o c k ( 1 , 1 )

T o p o f P i c t u r e


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DVCAM

Effect of a Head ClogEffect of a Head Clog

Digital Betacam

Clogged DVCAM HeadsClogged DVCAM Heads


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gggg


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Effect of a Dirty HeadEffect of a Dirty Head


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Effect of Poor TrackingEffect of Poor Tracking


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Effect of Low Tape tensionEffect of Low Tape tension


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Dirty capstan = poor tape handling = poor trackingDirty capstan = poor tape handling = poor tracking


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Dirty drum = poor recording and poor playbackDirty drum = poor recording and poor playback


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Dirty drum = poor recording and poor playbackDirty drum = poor recording and poor playback

Di id ki


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Dirty guide = poor trackingDirty guide = poor tracking

W i h ll


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Worn pinch rollerWorn pinch roller


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Customers DSR-20P deck!Customers DSR-20P deck!


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The Cassette ContactsThe Cassette Contacts


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Some cassettes have contacts on the rear edge of the shell -

Cassettes with contacts may or may not contain a memory chip.

Cassettes With MemoryCassettes With Memory


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Function of Contacts

11 22 33 44

Contact 1 VDD (2.7 to 5.5V)

Contact 2 SDA (Serial Data In/Out)

Contact 3 SCK (Serial Data Clock)

Contact 4 GND




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Function of Memory


The memory chip inside a Sony cassette has a capacity

of 16kbit (2kbytes).

The memory area from bytes 0 to 15 is called the Main

Area.

The remainder of the memory area is called the OptionalArea.



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M

ainA

rea

Option

alA

rea

APM BCID APM Application of Memory = 111 for a new cassette

BCID Basic Cassette Identification

Tape grade (consumer/non-consumer)

Tape type (metal evaporated/metal particle)

Tape thickness (7 micron/other)

Byte 0

Byte 15

Cassette ID

Tape Length

Cassette ID VCR/non-VCR

ClipLink

TC data

Cassettes Without MemoryCassettes Without Memory


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Cassettes Without MemoryCassettes Without Memory

Basic cassette information is identified by resistors connected

between Pin 4 and Pins 1, 2 and 3

Pin 4 1 Open circuit 7 micron tape

1.8 kohm Other

Pin 4 2 Open circuit Metal evaporated tape

1.8 kohm Cleaning cassette

Short circuit Metal particle tape

Pin 4 3 Open circuit Consumer grade tape

6.8 kohm Non-consumer grade tape

Cassettes Without ContactsCassettes Without Contacts


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Cassettes Without ContactsCassettes Without Contacts

These are read as 7 micron/Metal Evaporated/Consumer tapes.


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DVCAM HeadsDVCAM Heads


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A n a l o g u e

DVCAM Record ProcessDVCAM Record Process


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I n p u t

V i d e oS e l e c t

I n p u tA u d i oS e l e c t

S V i d e oC o m p o s i t eC o m p o n e n t

A n a l o g u eV i d e o I n p u t s

S D I

D i g i t a lV i d e o I n p u t s

A n a l o g u e

A u d i oI n p u t s

C h - 1C h - 2C h - 3C h - 4

C h - 1 / 2C h - 3 / 4

D i g i t a lA u d i o

I n p u t s


4 : 2 : 2 4 : 2 : 0 V i d e oC o m p r e s s

O u t e r E C C

O u t e r E C C

I n n e r E C C

S N R Z IE n c o d e r

2 4 - 2 5 B i tM o d u l a t o r

T a p

D VI n t e r f a c e

i . L I N K

Q S D I

A n a l o g uV i d e o O

DVCAM Playback ProcessDVCAM Playback Process


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V i t e r b iD e c o d e r

O u t e r E r r o r

D e t e c t

V i d e oD e - C o m p r e s s

I n n e r E r r o r

D e t e c t

O u t e r E r r o r

D e t e c t

T a p e I n t e r p o l a t o r 4 : 2 : 0 4 : 2 : 2V i d e o

O u t p u t

P r o c e s s

S V i d e oC o m p oC o m p o

V i d e o O

S D I

D i g i t a lV i d e o O

A n a l o g uA u d i oO u t p u t s

C h - 1C h - 2C h - 3C h - 4

C h - 1 / 2C h - 3 / 4

D i g i t a lA u d i oO u t p u t s

A u d i oO u t p u t

P r o c e s s

D VI n t e r f a c e

i . L I N K

Q S D I


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THETHE

XH2-1ASTXH2-1AST

TRACKING ALIGNMENT TAPETRACKING ALIGNMENT TAPE

T k i i f t i N o t r a c k i n g i n f o r


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ODD

EVEN

O D D T R A C KE V E N T R A

T r a c k i n g i n f o r m a t i o n N o t r a c k i n g i n f o r

O D D H E A DE V E N H E A D


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DVCAM EQUALISATIONDVCAM EQUALISATION

ADJUSTMENTSADJUSTMENTS

DVCAM EQUALISATION ADJUSTMENTSDVCAM EQUALISATION ADJUSTMENTS


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Phase

EqualiserCosine

EqualiserAGC

Viterbi

DecoderADC

PLL

RF from

PB head

Delay

Phase Cos AGC Delay

Data

Out

Phase

Frequency

Amplitude

Frequency

DataData

ClockClock

DVCAMformat

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