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printscreen

join:2003-11-01
Juana Diaz, PR
Reviews:
·Choice Cable TV
·Coqui/PRTC

DTV: How many sub-channels?

Although I normally watch cable TV I have always kept the outdoor antenna and have the capability of getting off-the-air tv if I want to. There is one local channel that used to have two additional sub-channels. They have their main programming on 4.1 in HD, a sports channel in 4.2 and a weather channel in 4.3. Recently the sports channel went HD and now 4.3 is no longer available off-the-air or in cable tv. Did they eat up all their bandwidth by going HD in their second channel?


ArthurS
Watch Those Blinking Lights
Premium
join:2000-10-28
Hamilton, ON
Broadcasters in North America have 19 Mbit/s to play with per channel, and depending on the compression schemes they use, can squeeze multiple sub channels in along with their main broadcast.

Scroll to the bottom of this page to see all the different combinations:
»en.wikipedia.org/wiki/Digital_subchannel

BoulderHill1

join:2004-07-15
Montgomery, IL
reply to printscreen
I find that occasionally the sub channels will change.

In my area we had NBC on 5.1 and then 5.2 also had a sports channel. 5.3 was weather/traffic.

Now 5.3 is gone.


Vchat20
Landing is the REAL challenge
Premium
join:2003-09-16
Columbus, OH
reply to ArthurS
said by ArthurS:

Broadcasters in North America have 19 Mbit/s to play with per channel, and depending on the compression schemes they use, can squeeze multiple sub channels in along with their main broadcast.

Scroll to the bottom of this page to see all the different combinations:
»en.wikipedia.org/wiki/Digital_subchannel

This. It is all basically bandwidth at this point. 19mbit/s total per transmitter and MPEG2 video. Divy up into how many subchannels you want based on bandwidth usage.

I've seen some with about 4 or 5 subchannels including the main. If someone desired to do solely music they could probably do like how Music Choice is operated on cable networks and fit in some ~40 channels with the right bitrate setup.

Where I used to live up in the Youngstown area, WKBN (at last check) runs both their channel (CBS) and WYFX (Fox, they own the channel as well) at 720p each on the same transmitter with a good encoder setup that does well keeping the quality up on both channels and squeezing them in the 19mbps allotment.

And with the development of Mobile DTV you now also have what is essentially an IP stream run OTA that feeds a youtube-like H264/AAC video feed meant for mobile devices and it runs in that same 19mbps limit.

All bits now flying through the air.

EDIT: One good site I would recommend looking at if you want to see some of the technical details: »www.rabbitears.info/market.php Drill down to a market and station and hit the TSReader data and it will show you the core details of the complete transmission.
--
I swear, some people should have pace-makers installed to free up the resources. Breathing and heart beat taxes their whole system, all of their brain cells wasted on life support.-two bit brains, and the second bit is wasted on parity! ~head_spaz


printscreen

join:2003-11-01
Juana Diaz, PR
Reviews:
·Choice Cable TV
·Coqui/PRTC
reply to printscreen
Thanks to all for the replies. Lots of interesting info in that rabbitears site although a bit ooutdated in the sub-channels and video details. The channel in question is at 1080i in the main 4.1 channel and 720p in the 4.2 channel which agrees with the Wikipedia reference. That explains why 4.3 is gone confirming my original question that they ate up all their badnwidth by going HD in the second channel.

There is another channel here that has its main HD channel .1 plus four additional SD video feeds. They later added their radio station in the .6 sub-channel and I now noticed that have an additional .7 channel but there is nothing there yet, just a blank screen.

I get 32 channels off-the-air which is similar to what basic cable had 20 years ago.


88615298
Premium
join:2004-07-28
West Tenness
Trying to put 2 HD channels on one channels just makes for 2 sub par HD channels. Just like 1 HD and more than 1 subchannel make for sub par HD but not as bad.


Vchat20
Landing is the REAL challenge
Premium
join:2003-09-16
Columbus, OH
It all depends on your POV on the matter. I won't say running 2 HD subchannels is going to be the BEST quality, but if you're more about the content and having 'decent' quality, it may be better to run the 2 HD's side by side.

Case in point: My prior mention of the station where I used to live which ran 2 720p channels side by side. In that particular case they ran both CBS and FOX in 720p with a well set up encoder that varied the bitrate constantly depending on which channel needed the bandwidth more at the time. Quality was 'good'. Not great, but good. About U-Verse quality. But the main reason for running both in HD was Fox's (WYFX) primary transmitter at the time was still a low power LD transmitter which did not reach most of their DMA when the digital switchover happened. Since WKBN owns WYFX, they rebroadcasted WYFX on WKBN's transmitter which had ridiculous power and range. I was glad to have Fox in HD albeit a bit degraded on quality, given I could not receive WYFX at all at the time.

Now though, I believe, is WYFX's main transmitter is more up to par for reception distance so they have went back to just an SD feed on WKBN's transmitter.
--
I swear, some people should have pace-makers installed to free up the resources. Breathing and heart beat taxes their whole system, all of their brain cells wasted on life support.-two bit brains, and the second bit is wasted on parity! ~head_spaz