Transcript MPEG-2 - University of Haifa

MPEG-2
Scalability Support
Nimrod Peleg
Update: Dec.2000
MPEG-2 Target
• “...Generic coding method of moving pictures
and associated sound for ...digital storage, TV
broadcasting and communication...”
• Dedicated for high quality services
e.g. HDTV, Networked data services etc.
• Eveloped from CCIR-601, CCIR-648, JPEG,
H.261 and MPEG-1 former standards
MPEG-2 Btstream structure
Sequence
Seq. Hdr.
Seq.
Ext.
Sequence
Ext.&User
Sequence
GOP
GOP
GOP Header Ext.&User Picture Data Picture Data
Pic. Hdr.
Pic. Coding Ext. Ext.&User
Slice Header Macroblock
Macroblock Hdr.
Block
Block
Slice
Slice
Macroblock
Block
Scalability Modes
 SPATIAL
SCALABILITY
 TEMPORAL SCALABILITY
 SNR SCALABILITY
 DATA PARTITIONING
SNR Scalability
 Refinement
of the DCT coeffs. encoded in
base layer by the enhancement layer coeffs.
 Base layer containes coarser quantization
then enhancement layer
 Only non intra quant. matrices are used in
the enhancement layer
 Enhancement layer contains coded
refinement DCT coeffs. and a small
overhead
SNR Scalability (Cont’d)
• DCT coeffs. in base layer are added to
DCT coeffs. in enhancement layer
• The combined layer decoding process
is identical to decoding of a nonscalable bitstream
• Different rate control for the 2 layers
SNR Scalability Scheme
Lower Layer Code
VLC
Inverse Scan
Inverse Quant
+
Enahncement Layer Code
VLC
Inverse Scan
Inverse Quant
Decoded Samples
Inverse DCT
Motion Compensation
Frame Storage
Memory
Data Partitioning
• The bitsteam is split into 2 layers:
partition0, partition1
• The Priority Breakpoint (in sequence
header) indicates which syntax elements are
placed in partition0 which is the base or
high priority partition
Data Partitioning
(Cont’d)
• The remainder of the bitstream is placed in
partition1 which is the low priority partition
• Seq.,GOP,picture and slice headers are
duplicated from partition0 to partition1
• VBV refers to the sum of the 2 partitions
• Partition0 contains sequence scalable extension
Data Partitioning
(Cont’d)
• No Data Partitioning
Quant DC
Scale coeff
DCT DCT DCT EOB DC
DCT EOB
coeff1 coeff2 coeff3
coeff coeff1
•Partitions for Priority Break Point 64:
Quant DC
Scale coeff
DCT DC
DCT
coeff1 coeff coeff1
DCT DCT EOB EOB
coeff2 coeff3
Partition0
Partition1
Data Partitioning
(Cont’d)
Possible Breakpoints:
• After slice header
• After macroblock address increment
(macroblock header)
• Before coded block pattern (after Motion Vector)
• After any number of DCT coefficients (excluding
one)