Originally Posted by Wendell R. Breland
You are thinking in terms of a linear compression encoder. One would assume IPTV that Netflix is using is bidirectional, that is to say the decoded can talk back to the source server and tell it certain parameters.
Multiple fixed encodes also sounds like a reasonable way to do IPTV. As I said earlier, it is very obvious to me many are using a very low frame rate.
What happens in these streaming network VOD systems is that they keep multiple encodings of the each title at different bit rates. They continously test the bandwidth available on the connection to your player, which may fluctuate. If available bandwidth decreases below what's necessary for the encoding currently in use, the server software selects a lower bit rate encoding and continues streaming with that; if the bandwidth should increase, it moves to a higher bit rate encoding. The best systems, like Zune Video, do this dynamic encoding switch seamlessly, without pause. You may notice the decreased or increased picture quality as these switches occur. Some of the Netflix players, like the Xbox one, try their best to make these transitions seamless, but they sometimes fail, and they put up a message telling you that they're rebuffering an alternate encoding (not in those words
Netflix keeps up to 6 encodings of every title, 4 standard def ones and, for a subset of titles, two 720p ones. They also keep a separate set of 4 or 6 encodings of each title in AVC with DD2.0 sound for the Playstation (all of the others use VC-1 encodings with stereo WMA sound). I think that they keep yet another set of encodings for the PC, being VC-1/WMA in a different format for a seamless-encoding-switching (aka "smooth streaming") web-based player for Windows and Macs.
To judge by the quality meter, there are at least five encodings for every HD streaming Zune Video title, 3 SD ones, one 720p and one 1080p. Every SD Zune title seems to have 4 encodings.
I tend to associate IPTV with systems which carry multiple channels of linear programming, just like cable or satellite. If you're watching one of these linear channels, you can't fast forward (though they probably all keep a local buffer of the linear stream from the point that you "tuned" it and you can FF or RW through that buffer). No doubt IPTV systems generally offer some VOD content in addition to linear channels, but I've never heard anyone other than you apply the term "IPTV" to these VOD-only services.