1. VIDEO COMPRESSION &VIDEO COMPRESSION &
MPEGMPEG
0992970-0992970- 楊凱翔楊凱翔
0992969-0992969- 林江瑜林江瑜
0992965-0992965- 連重凱連重凱

2. OutlineOutline
• VIDEO COMPRESSIONVIDEO COMPRESSION
– VIDEO CODING BASICSVIDEO CODING BASICS
– MOTION COMPENSATIONMOTION COMPENSATION
• MPEG FAMILYMPEG FAMILY
– MPEG-1 VIDEO standardMPEG-1 VIDEO standard
– MPEG-2 VIDEO standardMPEG-2 VIDEO standard
– MPEG-4MPEG-4
– H.264H.264
– MPEG-7MPEG-7

3. VIDEO COMPRESSIONVIDEO COMPRESSION
• Why do we use compression?Why do we use compression?
– Temporal RedundancyTemporal Redundancy
– Spatial RedundancySpatial Redundancy
time
x
y

4. Two Stage Coding ProcessTwo Stage Coding Process
Stage 1
Stage 2

5. Reducing TemporalReducing Temporal
RedundancyRedundancy
• Segment a frame into macroblocks, notSegment a frame into macroblocks, not
search by pixelssearch by pixels
• Output energy( bit rate) is increased withOutput energy( bit rate) is increased with
the degree of temporal redundancythe degree of temporal redundancy
• Interframe coderInterframe coder ( only use temporal( only use temporal
redundancy reduction)redundancy reduction)

6. Reducing Spatial RedundancyReducing Spatial Redundancy
• Using DCT codingUsing DCT coding
• Intraframe coderIntraframe coder (use only spatial(use only spatial
redundancy reduction, only for currentredundancy reduction, only for current
frame)frame)
• Hybrid( intra-/ inter - frame) coding methodHybrid( intra-/ inter - frame) coding method

7. Motion CompensationMotion Compensation
• Often used andOften used and
developed bydeveloped by
MPEG familyMPEG family
• 將相鄰的將相鄰的 frameframe 中中
出現的移動物件進出現的移動物件進
行互相補償的過程行互相補償的過程
，因為該物件移動，因為該物件移動
範圍不大且形狀在範圍不大且形狀在
短時間內不易變動短時間內不易變動
• It is preceded byIt is preceded by
motion estimationmotion estimation
Motion Vector
Search Range
Current Frame
Reference Frame
Ω

8. MPEG-1 IntroductionMPEG-1 Introduction
• DCT for intra- and inter- framesDCT for intra- and inter- frames
• Block-based motion compensationBlock-based motion compensation
• Huffman CodingHuffman Coding
• Source input format : YUV, why not RGBSource input format : YUV, why not RGB
• Y : luminance component(Y : luminance component( 亮度亮度 ))
• U(Cb), V(Cr) : color difference orU(Cb), V(Cr) : color difference or
chrominance componentchrominance component （色差）（色差）

9. MPEG-1 Picture TypeMPEG-1 Picture Type
• Intra-Picture( I )Intra-Picture( I )
• Predicted- Pictures( P )Predicted- Pictures( P )
• Bidirectional-Predicted-Picture( B )Bidirectional-Predicted-Picture( B )

10. MPEG-2MPEG-2
• 與與 MPEG-1MPEG-1 通用通用
• Difference from MPEG-1Difference from MPEG-1
– 好很多的畫質好很多的畫質
– 更多的輸入格式更多的輸入格式 ( ex: RGB, more YUV form)( ex: RGB, more YUV form)
– 在雙向傳輸時有較短的在雙向傳輸時有較短的 delay timedelay time
– Higher bit rateHigher bit rate
– We can adjust our pictures qualityWe can adjust our pictures quality

11. MPEG-4MPEG-4
• 針對整合多媒體、通訊、電腦之應用上，具體內針對整合多媒體、通訊、電腦之應用上，具體內
容則是以內容為基礎容則是以內容為基礎 (Content-based)(Content-based) 的應用上。的應用上。
• 將影片區分為前景及背景將影片區分為前景及背景（（ Object-BasedObject-Based ）），只，只
要記錄動態圖像的軌跡即可，因此在壓縮量及品要記錄動態圖像的軌跡即可，因此在壓縮量及品
質上，能較質上，能較 MPEG-1MPEG-1 及及 MPEG-2MPEG-2 來得更好，每秒來得更好，每秒
動態資料處理速率彈性更大。動態資料處理速率彈性更大。

12. Some MPEG-4 Video FeatureSome MPEG-4 Video Feature
• SegmentationSegmentation
• SpriteSprite
• TrackingTracking

13. MPEG-1 vs. MPEG-2 vs. MPEG-4MPEG-1 vs. MPEG-2 vs. MPEG-4
一般解析度
最大解析度
一般資料量
最大資料量
Mpeg-1
Mpeg-2
Mpeg-4
3Mbps
80Mbps
5~10Mbps
0.88Mbps
6.5Mbps
1.38Mbps
720X576
1920X1152
352X288
720X576
720X576
352X288

14. MPEG-1 vs. MPEG-2 vs. MPEG-4MPEG-1 vs. MPEG-2 vs. MPEG-4
影像規格影像規格 Mpeg-1Mpeg-1 Mpeg-2Mpeg-2 Mpeg-4Mpeg-4
壓縮能力壓縮能力 中中 中中 強強
檔案大小檔案大小 中中 大大 小小
影像品質影像品質 可可 很好很好 可至很好可至很好
網路傳輸網路傳輸 勉強勉強 不可能不可能 最佳化 最佳化