Overview of Digital TV cards for PC
Note: Due to file size and download time considerations, many of the sample images presented in this review have been converted to JPEG format and resized, which reduces the quality of the original image. Please keep this in mind when viewing the example images.
Digital TV Basics
As you may or may not know, Australian TV networks have been broadcasting a digital signal along with the analog one for several years now, and in a growing coverage area. Since the digital signal is compressed and far more spectrum efficient, it was promised to deliver some of the following extra features:- Multichanneling – the ability for one broadcaster to deliver multiple separate ‘video streams’. This could consist of entirely different programs, or perhaps a different camera angle at a sporting event.
- Widescreen - see movies, sports and TV shows in a wide 16:9 aspect ratio
- High Definition – programs that are broadcast at a much higher resolution
- High quality sound – digital formats including Dolby Digital 5.1
Unfortunately the digital TV signal is not very commonly received (due to equipment costs, lack of awareness, lack of incentive, etc), but a number of these features are being broadcast:- The Nine and Ten networks deliver a number of programs in High Definition, including “The Guardian”, “The Panel”, “Becker”, "GMA", "Totally Wild", "White Collar Blue", "Everybody Loves Raymond" (10), “Burgo’s Catch Phrase”, “McLeod’s Daughters”, “ER”, “Enterprise”, "Business Sunday", "Sunday", "Mornings with Kerri-Anne", "The Education of Max Bickford", "This is your life", "The Footy Show NRL", "The District", "The Parkers", "First Monday", "CSI Miami", "The Sopranos" (9), and some movies.
- All of the networks deliver a substantial amount of Widescreen Digital content (as you probably have noticed by the “Available in Wide Screen Digital” message). The majority of prime-time viewing is in Widescreen
- ABC delivers extra channels “FlyTV” and “ABC Kids” (UPDATE: These channels have been officially discontinued). The commercial broadcasters are not currently allowed to do this by law (but may still provide multiple camera angles at sports broadcasts)
- Electronic program guides are available
Please remember though, that not all of these features are available in all areas as of yet. As of writing, most of the High Definition for example was confined to Melbourne and Sydney. This will eventually change.
However, with a number of (comparatively) low-cost PCI cards just starting to appear on the Australian market, you can take advantage of a number of DTV features using your existing PC setup.
The Technical Details
The DTV signal is broadcast on a standard 7MHz chunk of spectrum on UHF and/or VHF close to the existing analog signals, so in most cases can be received with your existing antenna setup.
The DTV signal is COFDM (Coded Orthogonal Frequency Division Multiplexing) which means it uses a large number of carriers which are QAM modulated with pieces of the binary information. OFDM is quite resilient to multi-path interference and because the data is convolutionally coded and reordered it is also resilient to transient noise and a substantial amount of errors. (Convolutional coding rate on Australian networks varies from 2/3 to ¾).
How the Cards Work
The DTV cards that are starting to hit the market consist of a PCI card with an antenna connector, as well as usually an IR remote control and a USB IR receiver for the remote. The remote is used for controlling the TV software.
The PCI card receives the RF signal, locks onto the frequency specified by the user, demodulates and decodes the signal, and passes the information to the software which will decode the MPEG-2 video and/or audio.
Time-shifting
A very powerful feature of Digital TV on the PC is the ability to ‘time-shift’. Time-shifting allows the ‘pausing’ of regular TV, by diverting the stream to file (usually on hard disk). I’ll illustrate this by example:
I am watching a great TV program but am expecting an urgent phone call. The phone call arrives during the best bit of the program. I press the “pause/timeshift” button on the remote which freezes the program, but the software continues receiving the program and diverting to hard disk (you need plenty of space for digital TV, especially HD). When I return, I can simply press “pause/timeshift” button again to play back from the hard disk buffer (whilst the software continues to receive the program to this buffer). I then have the option to watch the program delayed, fast forward (through the ads!) and rewind at my leisure through the buffer, or return to the live stream by pressing “play”.
Recording
Another useful feature of Digital TV on the PC is the ability to capture programs to hard disk. Unlike analog TV tuner cards, no encoding is needed, the software can simply divert the MPEG-2 streams in their original form to a file on the hard disk, for playback with everyday software like Windows Media Player or WinDVD.
The streams can occupy a considerable amount of disk space (average size was 1M/sec for SD, 1.5M/sec for HD), but could be compressed using other codecs such as DivX, or burnt to DVD.
Most of the software offers the ability to program recording times in as well, just like an existing VCR. No more VHS tapes to be taped over or lost!
EPG (Electronic Program Guide)
The digital TV tuners can receive the programming schedules which are broadcast over the air in two forms:- As an actual video stream provided by the broadcaster
- In binary information which can be interpreted by the software
For example, in Melbourne, the Seven and Nine networks offer both types of EPG.
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