August 3rd, 2010
High-definition television (or HDTV) is a digital television broadcasting system with higher resolution than traditional television systems (standard-definition TV, or SDTV). HDTV is digitally broadcast; the earliest implementations used analog broadcasting, but today digital television (DTV) signals are used, requiring less bandwidth due to digital video compression.
High-definition display resolutions
| Video format supported | Native resolution (W×H) | Pixels | Aspect ratio (W:H) | Description | ||
|---|---|---|---|---|---|---|
| Actual | Advertised (Mpixel) | Image | Pixel | |||
| 720p 1280×720 |
1024×768 XGA |
786,432 | 0.8 | 16:9 | 4:3 | Typically a PC resolution (XGA); also a native resolution on many entry-level plasma displays with non-square pixels. |
| 1280×720 | 921,600 | 0.9 | 16:9 | 1:1 | Standard HDTV resolution and a typical PC resolution (WXGA), frequenlty used by video projectors; also used for 750-line video, as defined in SMPTE 296M, ATSC A/53, ITU-R BT.1543. | |
| 1366×768 WXGA |
1,049,088 | 1.0 | 683:384 (approx. 16:9) |
1:1 approx. |
A typical PC resolution (WXGA); also used by many HD ready TV displays based on LCD technology. | |
| 1080p/1080i 1920×1080 |
1920×1080 | 2,073,600 | 2.1 | 16:9 | 1:1 | Standard HDTV resolution, used by Full HD and HD ready 1080p TV displays such as high-end LCD, Plasma and rear projection TVs, and a typical PC resolution (lower than WUXGA); also used for 1125-line video, as defined in SMPTE 274M, ATSC A/53, ITU-R BT.709; |
| Video format supported | Screen resolution (W×H) | Pixels | Aspect ratio (W:H) | Description | ||
|---|---|---|---|---|---|---|
| Actual | Advertised (Mpixel) | Image | Pixel | |||
| 720p 1280×720 |
1248×702 Clean Aperture |
876,096 | 0.9 | 16:9 | 1:1 | Used for 750-line video with raster artifact/overscan compensation, as defined in SMPTE 296M. |
| 1080p 1920×1080 |
1888×1062 Clean aperture |
2,001,280 | 2.0 | 16:9 | 1:1 | Used for 1125-line video with faster artifact/overscan compensation, as defined in SMPTE 274M. |
| 1080i 1920×1080 |
1440×1080 HDCAM/HDV |
1,555,200 | 1.6 | 4:3 | 4:3:1 | Used for anamorphic 1125-line video in the HDCAM and HDV formats introduced by Sony and defined (also as a luminance subsampling matrix) in SMPTE D11. |
Standard frame or field rates
- 23.976 Hz (film-looking frame rate compatible with NTSC clock speed standards)
- 24 Hz (international film and ATSC high definition material)
- 25 Hz (PAL, SECAM film, standard definition, and high definition material)
- 29.97 Hz (NTSC standard definition material)
- 50 Hz (PAL & SECAM high definition material))
- 60 Hz (ATSC high definition material)
At a minimum, HDTV has twice the linear resolution of standard-definition television (SDTV), thus showing greater detail than either analog television or regular DVD. The technical standards for broadcasting HDTV also handle the 16:9 aspect ratio images without using letterboxing or anamorphic stretching, thus increasing the effective image resolution.
The optimum format for a broadcast depends upon the type of videographic recording medium used and the image’s characteristics. The field and frame rate should match the source and the resolution. A very high resolution source may require more bandwidth than available in order to be transmitted without loss of fidelity. The lossy compression that is used in all digital HDTV storage and transmission systems will distort the received picture, when compared to the uncompressed source.
Recording and compression
HDTV can be recorded to D-VHS (Digital-VHS or Data-VHS), W-VHS (analog only), to an HDTV-capable digital video recorder (for example DirecTV’s high-definition Digital video recorder, Sky HD’s set-top box, Dish Network’s VIP 622 or VIP 722 high-definition Digital video recorder receivers, or TiVo’s Series 3 or HD recorders), or an HDTV-ready HTPC. Some cable boxes are capable of receiving or recording two or more broadcasts at a time in HDTV format, and HDTV programming, some free, some for a fee, can be played back with the cable company’s on-demand feature.
The massive amount of data storage required to archive uncompressed streams meant that inexpensive uncompressed storage options were not available in the consumer market until recently. In 2008 the Hauppauge 1212 Personal Video Recorder was introduced. This device accepts HD content through component video inputs and stores the content in an uncompressed MPEG transport stream (.ts) file or Blu-ray format .m2ts file on the hard drive or DVD burner of a computer connected to the PVR through a USB 2.0 interface.
Realtime MPEG-2 compression of an uncompressed digital HDTV signal is prohibitively expensive for the consumer market at this time, but should become inexpensive within several years (although this is more relevant for consumer HD camcorders than recording HDTV). Analog tape recorders with bandwidth capable of recording analog HD signals such as W-VHS recorders are no longer produced for the consumer market and are both expensive and scarce in the secondary market.
In the United States, as part of the FCC’s plug and play agreement, cable companies are required to provide customers who rent HD set-top boxes with a set-top box with "functional" Firewire (IEEE 1394) upon request. None of the direct broadcast satellite providers have offered this feature on any of their supported boxes, but some cable TV companies have. As of July 2004, boxes are not included in the FCC mandate. This content is protected by encryption known as 5C. This encryption can prevent duplication of content or simply limit the number of copies permitted, thus effectively denying most if not all fair use of the content.
Table of terrestrial HDTV transmission systems
| Systems | ATSC | DVB-T | ISDB-T |
|---|---|---|---|
| Source coding | |||
| Video | Main Profile syntax of ISO/IEC 13818-2 (MPEG-2 – Video) | ||
| Audio | ATSC Standard A/52 (Dolby AC-3) | As defined in ETSI DVB TS 101 154 – as H.264 AVC and/or ISO/IEC 13818-3 (MPEG-2 – Layer II Audio) and/or Dolby AC-3 | ISO/IEC 13818-7 (MPEG-2 – AAC Audio) |
| Transmission system | |||
| Channel coding | |||
| Outer coding | R-S (207, 187, t = 10) | R-S (204, 188, t =  |
|
| Outer interleaver | 52 R-S block | convolutional (I=12, M=17, J=1) | 12 R-S block |
| Inner coding | rate 2/3 Trellis code | Punctured convolution code(PCC): rate 1/2, 2/3, 3/4, 5/6, 7/8; constraint length = 7, Polynomials (octal) = 171, 133 | |
| Inner interleaver | 12 to 1 Trellis code | bit-wise, frequency, selectable time | |
| Data randomization | 16-bit PRBS | ||
| Modulation | 8VSB (Only used for over the air transmission) 16VSB (Designed for cable, but rejected by the cable industry, cable TV uses 64QAM or 256QAM modulation as a de facto standard) |
COFDM QPSK, 16QAM and 64QAM Hierarchical modulation: multi-resolution constellation (16QAM and 64QAM) Guard interval: 1/32, 1/16, 1/8 & 1/4 of OFDM symbol Two modes: 2k and 8k FFT |
BST-COFDM with 13 frequency segments DQPSK, QPSK, 16QAM and 64QAM Hierarchical modulation: choice of three different modulations on each segment Guard interval: 1/32, 1/16, 1/8 & 1/4 of OFDM symbol Three modes: 2k, 4k and 8k FFT |