Video compression- multimedia - Computer Science Engineering (CSE) PDF Download

 Page 1


Naveen Aggarwal 
Page 2


Naveen Aggarwal 
? We need to compress video (and audio) in 
practice since:  
? Uncompressed video (and audio) data are huge. In HDTV, 
the bit rate easily exceeds 1 Gbps. -- big problems for 
storage and network communications.  
– For example: HDTV is 1920 pixels horizontally by 1080 lines 
vertically, at 30 frames per second. Hence, the total data rate 
required would be approximately 1.5 Gb/sec.  
– Because of the 6 MHz. channel bandwidth allocated, each 
channel will only support a data rate of 19.2 Mb/sec, which is 
further reduced to 18 Mb/sec by the fact that the channel 
must also support audio, transport, and ancillary data 
information.  
– As can be seen, this restriction in data rate means that the 
original signal must be compressed by a figure of 
approximately 83:1.  
Page 3


Naveen Aggarwal 
? We need to compress video (and audio) in 
practice since:  
? Uncompressed video (and audio) data are huge. In HDTV, 
the bit rate easily exceeds 1 Gbps. -- big problems for 
storage and network communications.  
– For example: HDTV is 1920 pixels horizontally by 1080 lines 
vertically, at 30 frames per second. Hence, the total data rate 
required would be approximately 1.5 Gb/sec.  
– Because of the 6 MHz. channel bandwidth allocated, each 
channel will only support a data rate of 19.2 Mb/sec, which is 
further reduced to 18 Mb/sec by the fact that the channel 
must also support audio, transport, and ancillary data 
information.  
– As can be seen, this restriction in data rate means that the 
original signal must be compressed by a figure of 
approximately 83:1.  
? The following compression types are 
commonly used in Video compression:  
? Spatial Redundancy Removal – Intra frame coding 
(JPEG)  
? Spatial and Temporal Redundancy Removal – Intra 
frame and Inter frame coding (H.261, H.263, MPEG)  
 
Page 4


Naveen Aggarwal 
? We need to compress video (and audio) in 
practice since:  
? Uncompressed video (and audio) data are huge. In HDTV, 
the bit rate easily exceeds 1 Gbps. -- big problems for 
storage and network communications.  
– For example: HDTV is 1920 pixels horizontally by 1080 lines 
vertically, at 30 frames per second. Hence, the total data rate 
required would be approximately 1.5 Gb/sec.  
– Because of the 6 MHz. channel bandwidth allocated, each 
channel will only support a data rate of 19.2 Mb/sec, which is 
further reduced to 18 Mb/sec by the fact that the channel 
must also support audio, transport, and ancillary data 
information.  
– As can be seen, this restriction in data rate means that the 
original signal must be compressed by a figure of 
approximately 83:1.  
? The following compression types are 
commonly used in Video compression:  
? Spatial Redundancy Removal – Intra frame coding 
(JPEG)  
? Spatial and Temporal Redundancy Removal – Intra 
frame and Inter frame coding (H.261, H.263, MPEG)  
 
? H. 261 Compression has been specifically 
designed for video telecommunication 
applications:  
? Developed by CCITT in 1988-1990  
? Meant for videoconferencing, video telephone 
applications over ISDN telephone lines.  
? Baseline ISDN is 64 kbits/sec, and integral multiples 
(px64)  
? Maximum combined delay for compression and 
decompression is less than 150ms. 
 
Page 5


Naveen Aggarwal 
? We need to compress video (and audio) in 
practice since:  
? Uncompressed video (and audio) data are huge. In HDTV, 
the bit rate easily exceeds 1 Gbps. -- big problems for 
storage and network communications.  
– For example: HDTV is 1920 pixels horizontally by 1080 lines 
vertically, at 30 frames per second. Hence, the total data rate 
required would be approximately 1.5 Gb/sec.  
– Because of the 6 MHz. channel bandwidth allocated, each 
channel will only support a data rate of 19.2 Mb/sec, which is 
further reduced to 18 Mb/sec by the fact that the channel 
must also support audio, transport, and ancillary data 
information.  
– As can be seen, this restriction in data rate means that the 
original signal must be compressed by a figure of 
approximately 83:1.  
? The following compression types are 
commonly used in Video compression:  
? Spatial Redundancy Removal – Intra frame coding 
(JPEG)  
? Spatial and Temporal Redundancy Removal – Intra 
frame and Inter frame coding (H.261, H.263, MPEG)  
 
? H. 261 Compression has been specifically 
designed for video telecommunication 
applications:  
? Developed by CCITT in 1988-1990  
? Meant for videoconferencing, video telephone 
applications over ISDN telephone lines.  
? Baseline ISDN is 64 kbits/sec, and integral multiples 
(px64)  
? Maximum combined delay for compression and 
decompression is less than 150ms. 
 
The basic approach to H. 261 Compression is summarised as follows:  
 
•Decoded Sequence  
 
 
 
 
 
 
 
 
 
•Frame types are CCIR 601 CIF (352x288) and QCIF (176x144) images with 
4:2:0 subsampling.  
•Two frame types: Intraframes (I-frames) and Interframes (P-frames)  
•I-frames use basically JPEG  
•P-frames use pseudo-differences from previous frame (predicted), so frames 
depend on each other.  
•I-frame provide us with an accessing point.