TheRover said:
I have question, what is the maximum number of program streams that a TV station can broadcast ? I have seen up to 5 streams broadcasting at one time, but some websites state there could be 6.
There is no hard-and-fast limit. (I suppose at some point your minor-channel number gets too many digits for some receivers to handle it. That certainly won't happen before 99 programs)
What you get with an over-the-air DTV signal is a 19.2MBPS pipe. You can split that up however you want.
All streams are compressed. (you can't even fit one SD stream in 19.2MBPS without compression) The more streams you transmit, the more compression you need. (and the worse each stream works) It should be noted some types of stream compress VERY well; you can fit more of these in.
- standard-definition compresses better than HD.
- Programs where the video doesn't move much compress better than streams with lots of motion.
- It's possible to transmit audio-only streams -- with no video -- which require MUCH less of your 19.2MBPS than video.
Milwaukee Public TV is broadcasting a classical-music stream and a jazz stream. For both, the video is a static slide with information about the selection currently on the air. These would compress very well.
I think most engineers will tell you one HD program and one SD work well; two HDs, or up to six SDs, will also work decently. Some stations have tried quite a bit more, though the quality suffers. (one station here is running one HD and two SDs; one of the SDs is pretty ugly.)
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PTboardOp94:
There is generally a separate (MPEG) encoder for each stream.
There is however also a stream multiplexer, which combines the encoded programs for each stream into a single stream of data to go to the transmitter. This would indeed be a limiting factor. The one our station uses, IIRC it has eight inputs. (we're only using one) Some (many) multiplexers accept streams via Ethernet; I would think the number of possible streams would be essentially unlimited (again, within the 19.2MBPS limit) with something like this.
