Cavlc Decoder Final

8/13/2019 Cavlc Decoder Final

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PATEL GAURAV M (11EC65RO4)

SANDIKA BISWAS (11EC65R11)

RAWOCHAN KASOMWOSHI (11EC65R17)


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CAVLC DECODING STEPS

Coeff_token (TotalCoeffs &Trailing_ones)

Sign of Trailing ones

Level Decoding

Total Zeros Decoding

Run Before Decoding


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Decoding Coeff_token

( TotalCoeffs & Trailing_ones)

The total number of nonzero coefficients and the

number of trailing ones without sign are decoded Parameter N ((Nu+Nl)/2) decides VLC table to be

referred

Nu & Nl are nonzero coefficients in upper & left

Macroblocks respectively The code segment is searched into the table to find the

values of TotalCoeffs and TrailingOnes


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Selection of table

N Table

0,1 Num_VLC02,3 Num_VLC1

4,5,6,7 Num_VLC2

8 and above Num_FLC


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Example Input :

'000000011010001001000010111001100

N=0 Num_VLC0 Code found :

0000000110

TotalCoeffs = 5

Trailing_ones = 1

Code remaining :

10001001000010111001100


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Decoding Sign of TrailingOnes Each TrailingOnes decoded in reverse order

0 +1 1 -1

Example:

input: 10001001000010111001100

code found: 1

Trailing one : -1

Code remaining : 0001001000010111001100


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Decoding Level

Each level decoded using Level_VLC table

For the first coefficient Level_VLC0 is used

For further coefficients next tables are used basedon the thresholds as given below

Current VLC table Threshold to incrementtable

VLC0 0

VLC1 3

VLC2 6

VLC3 12

VLC4 24

VLC5 48

VLC6 N/A (Highest table)


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Special case:If number of trailing 1s are less than 3 the first decoded

nonzero level is decremented if negative and incrementedif positive.

Example : Input :

'0001001000010111001100 Code found

0001 (VLC0) -2 -3 (special case)0010 (VLC1) 3

00010(VLC1) 4111 (VLC2) -2

Code remaining :

001100


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Decoding TotalZeros TotalZeros is the sum of all zeros preceding the highest

non-zero coefficient in the reordered array

TotalZeros are decoded from TotalZeros_VLC table

using already encoded TotalCoeffs

Example:

input: 001100

code found: 0011

TotalZeros : 2

Code remaining : 00


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Decoding run_before run_before is the number of zeros which leads every

nonzero coefficient

For decoding a run_before_VLC table is used Table is determined by zeroleft

zeroleft is initialised with TotalZeros

zeroleft is updated by subtracting previous runbefore

from zeroleft


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Special cases:1. [run_before] = TotalZeros

2. run_before for the final (lowest frequency) non-zero coefficient

Example: Input:

00Run_before:

2

Final Output:-2 ,4, 3, -3, 0, 0, -1, 0, 0, 0, 0, 0, 0, 0, 0, 0

Rearranged coefficients

0 3 -1 00 -1 1 01 0 0 00 0 0 0


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References[1]. Iain E.G. Richardson, H.264 and MPEG-4 Video

Compression video coding for next generationmultimedia, John Wiley & Sons, 2003, pp.187-207.

[2]. Venkata Rao. Kakani, Implementation of VLSIArchitecture for the H.264/AVC Video codec , IITKharagpur, May 2009.

[3]. Joint Video Team (JVT) of ISO/IEC MPEG and ITU-T

VCEG, Draft ITU-T Recommendation and Final DraftInternational Standard of Joint Video Specification(ITU-T Rec. H.264 | ISO/IEC 14496-10 AVC),March2003

Cavlc Decoder Final

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