Vince writes:
Could you place (or give a link) on your blog the local TV stations bit rates that I have variously seen in your articles to the Canberra times?
Why not? First, though, I should note that the following figures were derived from some ad hoc recordings I made of digital TV broadcasts between September and November this year. There’s no guarantee that they’ll be the same next month. Indeed, the rates could conceivably be changed on a daily basis: higher rates in the evening and so forth.
The figures were obtained simply. Just record a chunk of a broadcast using a Topfield TF5000PVRt digital TV receiver, then look at the information it provides: program length in minutes and file size in megabytes. Divide the latter by the former and make appropriate adjustments to convert to megabits per second, and you have the answer. The figure includes the audio, the subtitles and any data validation/decoding material
By way of comparison, DVD’s have a top rate of just under 10 megabits per second (Mbps), and of the 500-ish titles I’ve measured, the average for a movie ranges from a high of 8.84Mbps (The Day the Earth Stood Still) to a low of 2.8Mbps (the Force Video version of Metropolis) The great majority are in the range of 4 to 7 Mbps.
Finally, all these come from the Tuggeranong retransmission tower in the South of Canberra. No telling what the figures may be elsewhere.
(Table over Fold)
| Channel | Description | Minutes measured | Bitrate (Mbps) |
|---|---|---|---|
| ABC TV Canberra | Main transmission channel for ABC TV in Canberra. Note that there are two audio streams on this station: MPEG and Dolby Digital. | 243 | 6.73 |
| ABC TV 2 | This, and ABC TV 3 and 4, all simply replicate ABC TV Canberra, minus the Dolby Digital audio. | 65 | 6.26 |
| ABC HD | True high definition, 1080i video. | 68 | 14.2 |
| ABC DiG Radio | No picture, just two channel MPEG audio at, seemingly, around 300kbps. | 13 | 0.31 |
| PRIME Canberra | Main transmission channel for Prime TV in Canberra, our Channel 7 affiliate. | 74 | 8.18 |
| Prime View 2 | This, and Prime View 1, are only occassionally utilised. During the Olympics one of these showed the action in a statistics/info box. Right now both these stations are showing the aftermath of the Melbourne Cup horse race, exactly the same as on PRIME Canberra. Normally, though, these are simply blank, aside from some text referring viewers to the main station. These figures are for when that was the case. During the Melbourne Cup broadcast, the bitrate was the same as on the main Prime station. | 64 | 1.72 |
| SBS DIGITAL 1 | Main transmission channel for SBS TV in Canberra. Note that there are two audio streams on this station: MPEG and Dolby Digital. | 80 | 4.79 |
| SBS DIGITAL 2 | Secondary transmission channel for SBS TV in Canberra. Mostly carries foreign news services. | 120 | 3.48 |
| SBS EPG | So-called Electronic Program Guide. In fact, it is merely a non-interactive sequence of graphics/text stills with news headlines and information about forthcoming programs. It carries a musical accompaniment. | 47 | 1.87 |
| SBS HD | This is SBS’ so-called High Definition station. It meets the government legal definition by virtue of being 576p (progressive scan), but in reality is not truly high definition. It carries the same programming as SBS Digital 1 | 58 | 7.89 |
| SBS RADIO 1 | No picture, just two channel MPEG audio at, seemingly, around 160kbps. | 20 | 0.16 |
| SBS RADIO 2 | As per SBS Radio 1 | 27 | 0.17 |
| SC10 Canberra | Main (and only) channel for Southern Cross Capital 10, Canberra’s Channel 10 affiliate. | 522 | 6.22 |
| WIN TV Canberra | Main channel for WIN TV, Canberra’s Channel 9 affiliate. | 114 | 7.04 |
| WIN TV HD | WIN High Definition (1080i) service. Last time I checked, this was a loop demo tape. | 61 | 12.16 |
In case you’re wondering, no the Topfield won’t display high definition broadcasts. But it will record the bitstream, so the figures for the three HD stations are more or less valid.