BBC cuts HDTV bit-rate

Data rates on Freesat have been ramped down - now below ten megabits per sec for H.264 - this is likely to reflect what Freeview HD will look like when Mux-B gets fired up from Crystal Palace this December.

Danielle Nagler, the recently-appointed head of BBC HD, admitted that the BBC had reduced the HD channel’s bit rate. She claimed that there was no evidence that a reduction in bit-rate reduced the picture quality.

I have to say that if you're the head of HD for probably the most prestigious broadcaster in the world and you believe there is no correlation between bitrate and perceived picture quality then you got the job under false pretenses as you know nothing about the technicalities of DVB.
Why didn't they give me that job! I know pretty much everything about SD, HD, DVB-T, OFDM, QAM etc etc!

It reminds me of the facilities (oh, and Quantel!) that used to claim 8-bits was better than ten!

ITV DVB-T stations - poor film transfers

Twice in the last couple of weeks I've sat down to watch a favorite film and realized what a terrible job ITV do when it comes to ITV 3 & 4 (actually - a few months ago the copy of Bill & Ted's Excellent Adventure I watched with the kids on ITV 2 was similarly afflicted).
The Scarlet Pimpernel (the 1982 romp with Jane Seymour and Anthony Andrews; "Sink me, your tailors have betrayed you"!) last week and Clint Eastwood Unforgiven about a month ago were both put out in 4x3 with very clear 1" C-format artifacts on them. Hasn't it been fifteen years since we started to do film transfers at 16x9? Wasn't that mandated by Ofcom when the Beeb saved DVB-T in this country from ITV's incompetence in the OnDigital debacle? Relying on telecine sessions you did back in the early nineties just won't do now - and even if you do have the cheek to just copy the 1" transfer to DigiBeta at least have the courtesy/engineering ability to line up the last VPR3 in your transfer area!

One DVB-T upgrade that's close to my heart!

This must be a new antenna in anticipation of DVB-T2 as The Wrekin has been carrying digital TV for years (my parents get their Freeview from The Wrekin). The Shropshire Star is their local tabloid and their pictures are quite good. You can see some a picture I took of the same transmitter a couple of years ago here and I couldn't miss the chance to quote a bit of Housman.

ON Wenlock Edge the wood’s in trouble
His forest fleece the Wrekin heaves;
The gale, it plies the saplings double,
And thick on Severn snow the leaves.

The how and why of COFDM

Coded Orthogonal Frequency Division Multiplexing (COFDM) is a form of modulation which is particularly well-suited to the needs of the terrestrial broadcasting channel. COFDM can cope with high levels of multipath propagation, with a wide spread of delays between the received signals. This leads to the concept of single-frequency networks in which many transmitters send the same signal on the same frequency, generating “artificial multipath”. COFDM also copes well with co-channel narrowband interference, as may be caused by the carriers of existing analogue services.

This is a very well written explanation of COFDM (as used in both digital terrestrial television and digital radio in the UK) - the workings of the multi-carrier system was something that I never really understood but this opened my eyes (did you realise that every DVB-T mux uses more than 6,000 carriers!). Recently I was explaining to someone how Viterbei decoders work (with particular reference to Digital Betacam VTRs) - again, I didn't realise that COFDM uses a modified Viterbei decoder (the 'soft viterbei decoder').
I wish I hadn't specialised in post-production so early as there are many things the the broadcast chain that I'm rusty/ignorant of.

My new DVB capture card, part 2 - It's working out well but there are a couple of issues worth noting;

• The card has to have a unique IRQ assigned to it. Now with the machine I put it in the P&P BIOS insisted on giving it the same interrupt as at least one other card. I tried all the tricks and eventually (in the last PCI slot - why is it always the last?!) managed to get it hogging the same interrupt as the onboard USB. I could do without USB so disabled it and we were nearly there.
• The card is demanding when capturing from the Freeview feed (why? it isn't having to decode/re-encode any video, just file away the MPEG2 stream as delivered) - I suppose extracting a stream from the 38meg MUX is a pretty clever thing to do.
• I get much better TiVO-style live TV pause when driving the display at 16 bit colour rather than 32 bit (millions of colours). The resolution seems irrelevant as does driving the video overlay surface directly or via DirectDraw - that confused me.
• On the AMD Athlon XP1700 chip there is just enough poke - if I hit that machine over the network for either file transfer or VNC while it's recording it drops frames. I've got a couple of bids on eBay for XP1900 chips at the moment!
• Media Portal looks like a good alternative to Compro's app (which is fine) - Saul has good things to say about Media Portal (even going as far as saying it's better than Windows MediaCentre!). Two of the things they recommend is starting from a fresh XP install and using a different drive for capturing to that where your Windows swap-partition is located. I think I'll give those recommendations a go.

So - I have captured a few things (including four hours of french tuition programmes on BBC2) with success but I feel I sailing a bit close to the wind performance wise - gotta defrag that partition again!