October 31, 2009

BBC HD PQ - new post on BBC Blog

Head of BBC HD Danielle Nagler has posted again on the BBC blog. She comments on the current issues but not really in much detail:
"Picture quality: I know this is a big concern for some of you, and honestly, I don't need lots of complaints to start to worry about this. I'll defend to the hilt a programme like Criminal Justice, which I think looked fantastic, though others are entirely within their rights to dismiss the "film look" that it went for. But of course I want to make sure that we keep up the standards of the HD offer from the BBC, and I want to make sure, through looking at both technical and audience filters (pardon the pun), that we are in good shape.

"I've launched some further work around this - not because I believe there is a problem, but because I want to make sure there is not - and together with Andy Quested I will of course bring you the outcomes of that work as soon as I can."

Full blog post here.

I can assure Danielle that there definitely is a problem: there is a significant difference in picture quality between her channel and the other HD channels such as National Geographic or FX. There's actually less difference between BBC1 and BBC HD - that cannot be right.

(Incidentally, I recorded Criminal Justice off BBC1 and thought the PQ there was pretty dull and muted - it's not something I would have held up as an obvious example of the problems with BBC HD at the moment as the source material wasn't ever going to be a good showcase. Life, however, should look stunning. And doesn't. I hope when they sort out the encoder/bitrate problem they re-broadcast it.)


Rowan said...

Does the V+ not reencode when you record a show? IIRC there are "quality" setting in the V+ menu. Even on highest quality it may look worse than watching it live, if its still reencoding. Anyway, something to perhaps consider if you're going to comment on the PQ of shows.

Nialli said...

Interesting point. There's no quality setting I'm aware of with the V+ - it just records at what my DVD recorder calls "SP" - 2gb for an hour of SD, 8gb for HD. (The V+ has a 160gb hard disc.
As both programmes I was comparing (Wild Russian and Life) were recorded, any degradation through re-encoding would be common, so I guess the comparison's still valid.
Incidentally, watched The Thick of It in HD last night on BBC HD then played back my BBC2 recording straight after - the latter was actually a better picture. Most odd.

ChrisD said...

I believe the V+ box records the broadcast stream directly, That is why it is encrypted as you have a perfect digital copy of the source data. So when you play it back you get exactly how it looked when broadcast.

Lewpy said...

What you do need to remember is the website that publishes bitrates does so for satellite broadcasts, not for cable.
Now, VM broadcasts HD in MPEG2 at the moment, so is probably re-encoding the BBCHD feed to make it "compatible" with their broadcast codec (BBCHD uses MPEG-4.2.0, iirc, same as SkyHD). What we don't have is any information on how this process is performed, and the subsequent bitrate VM then broadcasts the channels at.
If it comes in at 9Mbit/s MPEG4, and VM recodes it to 9MBit/s MPEG2, then PQ will suffer. MPEG4 is designed to perform better at lower bitrates than MPEG2.

Maybe the codec changes at the BBC have caused an issue with the re-encoding that VM does? Maybe that process can be examined by someone in the know :-)

andy said...

Web casting, or broadcasting over the internet, is a media file (audio-video mostly) distributed over the internet using streaming media technology. Streaming implies media played as a continuous stream and received real time by the browser (end user). Streaming technology enables a single content source to be distributed to many simultaneous viewers. Streaming video bandwidth is typically calculated in gigabytes of data transferred. It is important to estimate how many viewers you can reach, for example in a live webcast, given your bandwidth constraints or conversely, if you are expecting a certain audience size, what bandwidth resources you need to deploy.

To estimate how many viewers you can reach during a webcast, consider some parlance:
One viewer: 1 click of a video player button at one location logged on
One viewer hour: 1 viewer connected for 1 hour
100 viewer hours: 100 viewers connected for 1 hour…

Typically webcasts will be offered at different bit rates or quality levels corresponding to different user’s internet connection speeds. Bit rate implies the rate at which bits (basic data units) are transferred. It denotes how much data is transmitted in a given amount of time. (bps / Kbps / Mbps…). Quality improves as more bits are used for each second of the playback. Video of 3000 Kbps will look better than one of say 1000Kbps. This is just like quality of a image is represented in resolution, for video (or audio) it is measured by the bit rate.