MS Duhan, Deputy Director General (E), DG, DD, New Delhi

Video quality has generated huge interest among viewers of the modern-day society. The high quality of video has various aspects to be addressed by equipment manufacturers and broadcasters. An uncompressed video signal of HDTV has a bit rate of 1.485 Gbps, which is a huge data. It would fill up a 256-GB hard drive in just under 22 minutes. In case of ultra-high-definition (UHD) the data rate will be around 4 TB. This is a formidable bit rate and requires special storage and transmission system components and a very careful choice of interconnecting cables, connectors, circuit wiring, etc. So compression techniques have been evolved to mitigate the requirement of data storage and transmission. Compression of video data is a reversible conversion (encoding) of data that contains fewer bits. This allows more efficient storage and transmission of the data. The inverse process is called decompression (decoding). Software and hardware that can encode and decode are called Codec.

Video resolutions, bit rates, and bit depth are critical parameters of video data. Resolution is the number of pixels in the image. Bit rate is how much space is used for a given second of recording. As a coarse overstatement, the more space allotted, the more information one will be able to squeeze in there. Bit depth is how detailed the color is reproduced, as into how many decimal places. Compression is achieved by removing redundant information from the video sequence. Not all video data are equally significant from a perceptual point of view. Technical standards make use of the properties of the human visual system.

History of Compression

The MPEG-1 (Moving Picture Experts Group) standard was published in 1992 and its aim was to provide VHS quality with a bandwidth of 1.5 Mbps. In 1994, MPEG-2 was released, which allowed a higher quality with a slightly higher bandwidth. MPEG-2 is compatible to MPEG-1. MPEG-4 (H.265) was released in 1998 and it provided lower bit rates for a good-quality video. High-efficiency video coding (HEVC), also known as H.265, is the latest video compression standard. In comparison to MPEG-4 (H.264 AVC), HEVC offers about double the data compression ratio at the same level of video quality, or substantially improved video quality at the same bit rate. The first version of HEVC was published in June 2013. The second version was published in early 2015. Additional 3D-HEVC extensions for 3D video were completed in early 2015. HEVC supports resolutions up to 81924320, including UHD-8K. HEVC will thus provide a flexible, reliable and robust solution, future proofed to support the next decade of video. Due to more than 50 percent efficiency compared to MPEG-4, it reduces the payload requirements globally besides mitigating the requirements of UHDTV-4K and 8K. It can boost to generate immersive video, 3-D video, etc. Ultra-high-definition television includes UHD-4K (2160p) and UHD-8K (4320p), which are two digital video formats that are approved by the International Telecommunication Union (ITU).

Field Trials

Japan, Korea, France, UK, Czech Republic, Slovakia, Spain, Sweden, etc., have already experimented to transmit UHD-4K; most of them carried field trials using HEVC and DVB-T2 for terrestrial TV in UHF band. Only 9 months earlier, the bit rate required for UHD-4K used to be about 25–30 Mbps using HEVC. But of late, it has come down typically to 12–15 Mbps. It is a big motivation for broadcasters for their economic spectral usage and viable broadcasting of high-resolution video data. So DTH and digital terrestrial platforms may provide an excellent picture quality in times to come.

Motivation for Higher Codec

  • l In India, there are about 70 HDTV channels being transmitted by various operators on DTH Platforms. These include various genres like sports, movies, Hindi GEC, English GEC, infotainment, music, kids, regional, etc. So far, only one broadcaster has experimented for a program channel for UHDTV in India, but the days are not far when there will be plenty of such channels. Efficient codecs are essential for it.
  • lVideo exceeds half of Internet traffic and is expected to grow to more by end of 2016. With the increase in applications, content, fidelity, etc., it is expected that mobile data tariff will enhance 25 times during the next half decade. Video constitutes more than 50 percent in such usages. The XXXII Olympiad to be held in Tokyo in 2020 is expected to be covered in UHD-4K or even UHD-8K. All it requires is increased coding efficiency for optimal economics.
  • lStress on storage and transmission spectrum has pushed to innovate and develop new compression technologies.

Compression techniques have experienced quite revolutionary innovations and at a fast pace. It has significantly impacted equipment manufacturers, the broadcasters, and viewers as well. With DVB-T2 and HEVC, three TV program channels in UHD-4K or nine HDTV program channels can be relayed. The video landscape is under fast evolution and content broadcasting environment is bright and full of promise. Year 2020 is expected to see a new zenith in video quality.

Typical Video Bit Rates and Codecs

Video Format

Codec Standard

Compressed Data(Typical)

SDTV

MPEG-2

4-6 Mbps

MPEG-4

2-3 Mbps

HEVC

1.5-2 Mbps

HDTV

MPEG-2

14-16 Mbps

MPEG-4

7-8 Mbps

HEVC

3.5 to 4.5 Mbps

UHDTV

MPEG-2

-

MPEG-4

@30 Mbps

HEVC

12-14 Mbps