Yep - I think people assume that making a new ITV region HD on terrestrial just needs a new 'feed' of that region, ignoring that if that is a new unique combination of channels EVERY channel in the PSB3 mux (BBC One HD, BBC Two HD, ITV HD, C4 HD, C5 HD etc.) will require a new encoder (even if its carrying the same content already being encoded elsewhere) and for redundancy, that will mean two new sets of encoders, plus a new unique combination of services will also need dual redundant fibre distribution to the transmitters taking it
Is that right? Why do they have to seperately encode each service seperately for each mux?
BBC News Channel for example is the same everywhere, so surely they can just encode it for DTT
using several redundant encoders) and then use that to provide that for each Mux? Is it just a redundancy thing?
Because DTT Uses stat muxing it needs each if the services in a mux to have its own coder ... it's what enables (to use the PSB 3 HD mux as an example) a service to have 15++ Mbit/sec when it needs it to hold quality
... while most of the time taking say 3 to 4 Mbit/s
So if you split off a channel to be fed to all regional muxes what constant bit rate do you give it and thus subtract from the statmuxed pool ...
if you said say 8 Mbit/sec that would mean that the statmuxed pool would have
one fewer channel
and also some if the statmuxed gain would be lost ...
so probably not a good thing !
And if you turn it around if you stat mux the uk wide channels and the drive a encoder per region to complete the mux ... but the regional coder only gets the bit rate that's left which is not the quality that would be sought for a premier channel like a PSB .. but there are some things that you can do to improve the quality but it gets so complex ..and not predictable.
You then get into the realm Of the Transmux that I described fr Woolacombe ... but I have not seen one in AVC .... it was mind bendingly complex in MPEG 2.
Hence a set of coders statmuxing for each region is more or less the only way
but at a cost. ( times number of regions )
Just to make it more complex the DTT Hd mux uses two pass encoding so it is coding once and then seeing if it can make it better by using a different encoding toolset / bit rate ....
Last edited by Technologist on 9 July 2019 11:35am