Digital signal processing within digital televisions (DTVs) has advanced significantly, resulting in improved picture and audio quality. Further improvements in DTV technology over the next several years will continue to enhance the quality, but the largest gains in the HD video experience will be achieved by improving the A/V source received by the DTV. The video source, for example, is a highly degraded version of the original source captured in the studio. Improvements in the studio and broadcast infrastructure represent the greatest upsides for future quality improvements. This white paper examines the quality "hot spots" (degradation points) HDTV may suffer, from the time it is captured to the moment it is experienced by the consumer, and discusses ways of preserving and improving the quality within existing distribution bandwidth restrictions.
Enabling 1080p in the Studio for Full HD Quality
A DTV video studio environment contains various equipment, including video switchers and routers, storage servers, professional-grade cameras, and monitors, as well as recording, editing, encoding, and decoding equipment. The video switcher creates the video stream that is broadcast through television distribution channels, mixing live video from multiple cameras as well as prerecorded video from the storage servers, video tape or digital recorders (VTRs or VDRs), and editors to create a fluid video program (see Figure 1). Video switchers also feed studio monitors directly, allowing the user, most often a producer, to see the input and output video from the switchers. Video data is typically compressed and decompressed with MPEG or JPEG compression algorithms for storage or transmission to the end viewers.
Figure 1. Typical Studio Connectivity
Today's high-definition (HD) video studio environment must support a network of equipment operating at HD data-transfer rates. Production studios use coaxial cable to transport SMPTE259M (SDI) and SMPTE292M (HD-SDI) video and embedded audio between equipment. HD-SDI interfaces support data rates of up to 1.485 Gbps and are sufficient to handle HD resolutions associated with 1080I and 720p. However, the need for the higher quality full-HD video, enabled by 1080p, has increased bandwidth requirements.
Enabling 1080p, apart from improving the picture quality, has other benefits in video production studios. It is the highest level of resolution the standards enable and is free of the complexity and motion errors associated with interlace formats. Additionally, in North America and Europe, both 720p and 1080I formats are popular and are likely to coexist for the foreseeable future. This creates a dilemma for studios as to which format to use during production.
If the studios were to use 1080p during production, it would be easier to convert to 1080I or 720p without loss of quality. Fortunately, SMPTE recently ratified new 1080p standards that open up the bandwidth bottleneck of the SDI cabling used in studios. New SMPTE standards 424M (which defines the bit serial data format and the PHY characteristics of a 3-Gbps SDI link) and 425M (which defines the mapping of various formats for transmitting over SDI video on 3-Gbps link) leverage core technology improvements of FPGAs and PHY interface chips to double the SDI cable bandwidth from 1.485 Gbps to 2.97 Gbps, sufficient to support full 1080p serial video transport on a single link.