Originally Posted by SamVin
Actually in a 6 MHz broadcast channel the available data rate of a DTV television signal is 19.44 Mbps allowing up to six SD sub-channels to be transmitted.
19.393 Mbps. And the hard limit is actually 98 subchannels of any resolution, but at some point the quality degrades to the point of being unwatchable.
So WTRF has plenty of bandwidth to transmit one 720p HD and two 480 SD sub-channels.
It's arguable whether or not they can do it well, but "plenty" is the wrong word. It's a squeeze regardless.
The problem is as the allotted broadcast channel is divided for sub-channels the various compression ratios used to handle the data streams have to be adjusted correctly, especially during times when the amount of data spikes from rapidly changing content. The compression algorithms used work best on content that is either static or changes very little over time. When there is a lot going on in the content then the data can't be compressed as much, requiring more bandwidth in the sub-channel to transmit the data without error.
During those bursts a station engineer has to have allowed enough space in the sub-channel to handle this amount of data. And IMHO not all station engineers have mastered how to set that up correctly yet. Having seen that problem early on with other stations when they first went digital I feel that it is a skill that takes a bit of a learning curve.
You're making a faulty assumption that the total bandwidth demands will never exceed 19.393 Mbps (less, actually, given the other overhead that needs to be included in the stream). When multicasting, there will always be times when the video of all the subchannels combined will want more than the maximum bitrate available. At that time, something has to give and you get pixelization. There's nothing that can be done short of dropping the subchannels.
The best thing one can do is report it (respectively) to the station management when it occurs, so the station can try to get it corrected.
(My 2 cent's for what it's worth.
There may not be anything the station can do. They can buy a newer encoder assuming they don't already have the newest one, but even then there's only so much you can do to improve a defined standard like MPEG-2.