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Bit rates used on Freeview SD.
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Just a matter of my own personal interest does anyone know where I could get details of the bit rates, Kbps/Mbp,s used on Freeview SD both for audio and video ?
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Varies with channel and mux. If you have a box with recording capability and able to export recordings to a PC then Medianinfo will give you all the details.
If you are interested in a particular channel then I can check for you. It will have to be available in the Midlands (Lark Stoke)
PSB 1 is stat muxed, so the video bit rate for all channels will vary, although the coders will be set to 'floor' and 'ceiling' values which may well differ for each channel. (For instance BBC 1 having a higher values that BBC Parly).
I've got a feeling all six DTT muxes employ stat muxing ?
I'm pretty sure MarkC is right in that all muxes are now using stat muxing for the advantages it gives... and the above site shows that to be so (except the SDN mux would not display correctly for me).
A few years ago the other BBC channels were stat muxed but BBC1 operated at a high fixed bitrate. ISTR it was done to make the BBC1 regional opt-outs simpler. The other BBC channels could be stat muxed separately in London and the various regions then added BBC1 as required. (Special arrangements were made for the national variants of BBC2).
I'm just interested to know if/when this changed.
They are using big GOPs these days, the main PSB channels seem to be limited to 24 frames, but other channels range from the high 20s to 42 frames.
I think I remember rightly the standard GOP was once 12 frames, then the COM muxes started using 18 and up. This must be a big factor in the number of channels that can be carried. And with GOPs being variable they can sync with when the scenes change.
The price for more channels is slower channel changes, of course.
I think you may have been confused.
mpeg2 at that sort of bitrate is impossible for SD (720 x 576) and way beyond the capability of SD DVD/Digital TV.
mpeg2 can be used on Blu-ray at HD resolutions (1920 x 1080) but requires much higher bitrates than the more efficient H264/AVC codec which can produce excellent pictures with a good encoder at much lower bitrates.
...and stat muxing the whole mux.
The BBC one regionalality was added by having one coder in each region which was added (actually a drop add fir resilience) that coder fed the opt switch from either a decoder from a higher bit rate feed or the local studio.
ISTR reading a whitepaper about the old system on the bbc website. I don't know if there is anything similar for the new, I must have a browse sometime.
Interesting that the bitrate for TV sound is either 256kbps or 192kbps MPEG2 audio at 48kHz (DVD Quality) but DAB radio which uses the same codec is trying to convince everyone that 128kbps is all you need to transmit high quality stereo to the masses!
As one of the few people who actually thinks radio on Freeview is a good thing - I hope the BBCs choice of radio and bitrates is kept and not sacrificed (as with BBC Alba in Scotland) to bring in BBC One+1. DAB with its poor bitrates and mono R4X and R4 (sometimes) is just not a viable option - and not easily timeshifted. And I can't afford freesat, or excessive internet use.
This used to be the case for the English Regions, while The Nations were able to stat mux their whole portfolio (and use their own idents). Initially for digital TV, all but BBC One on the BBCA mux channels not being regionalised, were stat muxed from Crystal Palace, and distributed to the English regions. The MUX then also carried a fixed 7.5MB/sec version of BBC One London. The region could switch in or out their own fixed bit rate regional opt-out content to replace it.
Nowadays The Regions have progressed to be able to stat mux the entire portfolio on BBCA themselves. I'm not sure exactly what date the change took place.
The BBC moved all the Code & Mux kit to one location (well two - duplicate and diverse centres in fact) and the local programmes are 'switched to' as required.
All studio centres have duplicated feeds to the centre(s).
Twas some considerable time ago --- oh yes at DSO for each region (as the analogues no longer needed to go via the studios)!
It was 4.5 Mb/s, (7.5 would have been luxury !) Actually 4.5 looked pretty good.
I think in most cases, for most regions it was before DSO (in those regions) ?
I remember BBC 1 here in the South taking a drop in quality (and a drop in average file size on my PVR) well before our DSO (Feb 2012)
The interesting thing is there must have been a feed back to London from each region for Dsat uplink, or did they do that in the regions too?
No, the uplink was always done centrally in London. They took a copy of feed that fed the local DTT coder, and sent that back to London for D-Sat.
Now everything is coded and muxed in London (and another secret location) The Beeb could (but haven't yet) gone a stage further and copied ITV, by applying the opt out switch in London too. That
would remove the requirement for each region to have a quality network feed delivered to them. Advantages and disadvantages to either method. ITV Anglia experienced the disadvantage to London controlled opting a few years ago:-
http://www.youtube.com/watch?v=BkTV2Jza0xc
And with no one's marriage compromised, Meridian:-
http://www.youtube.com/watch?v=lI3uA-FgpH0