Digital TV video bitrates – May 2011

More advertising has recently hit our regional TV stations in the form of a channel called ‘GOLD’ using part of the WIN TV spectrum (it’s on Channel 84). Which, of course, prompts me to update the table of video bitrates. The last update was in September last year.

To gather this data, on 14 through 16 May I  recorded at least six hours, in three separate chunks, from each station onto a Topfield PVR. Then I whacked the minutes and megabytes into a spreadsheet, did the division and subtracted the audio bitrate. These figures probably overstate things a little, depending how much extra the Topfield adds into its recording stream (not much

, I imagine, because they are standard MPEG files), and the presence of subtitles. So, really, only the first two significant figures of the video bitstream should be considered.

Also, remember, this is in Canberra. The figures may well be quite different elsewhere. Our commercial stations still broadcast their HD as 1,440 x 1,080, for example.

If anyone would like to repeat the process in a major capital city, I’d be happy to email through the spreadsheet on condition that you provide the information back for publication here in due course.

Things to note:

• Several of the stations have changed their text names, usually just a little (‘Canberra GO’ is now ‘GO! Canberra’ for example)
• If you can believe the last table I did, then Prime has made significant technical changes to its advertising channel, 64. It has changed the display resolution from 720 x 576 to 544 x 576. Actually, I hadn’t realised that 544 is a valid horizontal resolution. Presumably Prime reckons that reducing the number of pixels by nearly 25% yields benefits in terms of reduced compression artefacts. It has also halved the audio bitrate to 128kbps, which is a sensible move since it will make little difference to the sound but those few extra bits might make a slight improvement to the video.
• The new station GOLD has an incredibly low video bitrate of less than 1.5Mbps! Again, the pixels have been reduced, with this one to 480 x 576, a full third below the norm. WIN has given it an audio bitrate of 192kbps, which is still a bit much, really. When you’re at video bitrates this low, even an extra 0.064Mbps could help.
• WIN still wastes lots of bits on audio for all its stations: 384kbps for the two SD ones and 448kbps for its HD station. Bringing the SD ones down to 192kbps would bring them into line with the bulk of 2.0 audio on DVD, and given that the HD is rarely if ever in 5.1 mode, 448kbps is a bit over the top.
• Southern Cross Capital (the 5* stations) and Prime (6*) seem to have a basically fixed bitrate for each of their channels, while the others seem to shift bits between channels, presumably according to need. The most extreme is ABC, which seems to boost the other channels (2, 22 & 24) overnight after its Kids Channel (23) shuts up. Oddly, it still uses a rather hefty 2Mbps for broadcasting a static panel on 23.
• The winner for HD bitrate — by a long, long margin — is One Canberra at 11.91Mbps. The next highest is SBS HD, a 720p station, with its routinely poor, upscaled SD. The other HD stations are around 8.5Mbps.
• The winner for SD bitrate is SC10 Canberra, closely followed by ABC1. But while SC10 was 5.14Mbps on all three clips, ABC1 was widely varied: 5.74, 5.05 and 4.57Mbps.