Noçoes de televisão compressão

Fundamentos em Compressão

REDE GLOBO_RJO Tektronix

1

Compression
MPEG - Moving Picture Experts Group

Six step process
• 1) • 2) • 3) • 4) • 5) • 6)
10 Bit to 8 Bit & 4:2:2 to 4:2:0 Intra-Frame Inter-Frame Discrete Cosine Transform (DCT)

Threshold & Quantization
Coding Run-Length & Variable-Length

2

November 15, 2007

MPEG Network Monitoring

INTRA-Frame Coding
Rate Control Quantizing Data

Full Bitrate 10-bit Data

Convert 4:2:2 to 8-bit 4:2:0

DCT

Quantize

Entropy Coding

Buffer

Compressed Data

Information lost No Loss Data reduced Data reduced Data reduced No Data reduced (information lost) (no loss) Stuffing

Entropy Coding Quantizing Reduce the number of bits for each coefficient. Variable Length Coding Run Length Coding Send a unique code Use short words for Give preference to certain coefficients. most frequent values word instead of strings Reduction can differ for each coefficient. of zeros (like Morse Code)

3

November 15, 2007

MPEG Network Monitoring

Group of Pictures
Bi-directional Prediction

Time
3 4 5 6 7

0

1

2

m = Distance between anchors n = Distance between I pictures

I

B

B

P

B

B

P

B

I

Forward Prediction I pictures: Intra-coding only P pictures: Contain forward motion compensation B pictures: Contain forward, backward & bi-directional motion compensation

4

November 15, 2007

MPEG Network Monitoring

Group of Pictures Motion Vectors

5

November 15, 2007

MPEG Network Monitoring

15/3 Frame Sequence
I B B P B B

Groups of 3 with 2 B-Frames between P-Frames Described as IBBP
P
B B P B B P

15 Frames between the I-Frames

B
B I

6

November 15, 2007

MPEG Network Monitoring

What is a Transport Stream ?
 A Transport Stream (TS) provides mechanism to transmit:
– – – – – – Multiple Video PES Multiple Audio PES Scheduling Information Closed Caption/Subtitles Private Data etc.

Multiplexed data onto