Information Technology Reference
In-Depth Information
consists of 4 sub-codecs for 3,840×2,160 images. A sub-codec contains four sin-
gle-unit MPEG-2 HDTV codecs and a multichannel frame synchronizer as de-
picted in Figure 8. To compress large images that exceed the resolution of HDTV
by using MPEG-2 video coding, the video format converter divides the SHV im-
age into multiple HDTV units. The HDTV coding conforms to MPEG-2 Main
Profile and 4:2:2 Profile @ High Level. Since motion vectors in higher resolution
images are often significantly larger than those in lower resolution images, it is
necessary to implement motion estimation with a wider search range in the en-
coder. The search vector range of the developed encoder achieves +/− 211.5 pixels
horizontally and +/− 113.5 lines vertically, exceeding existing common MPEG-2
encoders. The total coding delay is about 650 ms, which includes the process by
the encoder, the decoder and the video format converters.
Fig. 8
MPEG-2-based codec system
The multichannel sound signals can be transmitted in the form of uncompressed
linear pulse code modulation (PCM) (48-kHz sampling, 24 bits per audio sample).
In addition to the PCM, Dolby-E codecs with a compression ratio of 1:4 are also
equipped. They handle 24 audio signal channels for the 22.2 multichannel sound
system. The coded video and audio signals are multiplexed into four MPEG-2
transport stream (TS) signals interfaced via DVB-ASI (Digital Video Broadcast-
ing - Asynchronous Serial Interface).
The MPEG-2 4:2:2 Profile codec system can be used for improving transmis-
sion between the broadcasting stations and storage, since the codec achieves a bit-
rate of 600 Mbps with high image quality. A TS recording device that supports the
storage of long program material has also been developed. The storage capacity is
1.2 T bytes, which enables storage of a 4.5-hour-long program that is coded at 600
Mbps.
When public IP (Internet Protocol) networks are used for transmission of the
encoded SHV signals, consideration must be given to jitter and time delay depend-
ing on the transmission path. To synchronize the four TSs generated by the sub-
encoders, the system manages the timing of each video frame by means of a time
