NTL Digital Video Compression

[daniel larusso]

Hi, I recently purchased a £30 Digital Freeview box for the 28" widescreen TV in my dining room and have got to say that the picture is stunning and really pin sharp.

Now this has highlighted to me how pixelated and low quality the NTL picture is compared to the Freeview. Surely it should be the other way round? Watching a show like the X Factor or ANT and Dec on the NTL box is like watching a downloaded WMV file and is really blocky (especially when on the audience).

Just wondered if this is the normal or whether I should contact them about it. Is just a case of NTL cable digital using a high compression level?

Thanks

PS, also they seem to have stopped sending me invoices for the TV and Phoneline now. Seems they just take the money now

[bob_builder]

Originally Posted by daniel larusso

PS, also they seem to have stopped sending me invoices for the TV and Phoneline now. Seems they just take the money now

Yes, they do this to save paper if your bill is the same for three months running.

I noticed that ITV seemed to be utilising less bandwidth per channel on NTL than the BBC. I thought it would change when I got $ky but I think ITV is still more compressed than the Beeb. Still, it's infinetely better than some of the 'channels' I now have access to. I am very surprised, though, at how pixellated the Sky Sports channels can get ... I reckon you can't choose anything better than a football pitch to judge the quality of a digital TV picture and the Sky Sports pictures, to my eye, are no better than watching a game on ITV or C5 ... when the camera moves even a little, the players look like they're wading around on a bright green duvet instead of a grass pitch.

Offtopic, but I remember a similar discussion on here a while ago about DAB quality - that on digital radio, even the Beeb is going for quantity over quality and broadcasting streams that are effectively sub-FM standard on certain channels.

[SMHarman]

Originally Posted by Chris T

Offtopic, but I remember a similar discussion on here a while ago about DAB quality - that on digital radio, even the Beeb is going for quantity over quality and broadcasting streams that are effectively sub-FM standard on certain channels.

Certainly are, from wiki
Currently, 98% of all stereo radio stations on DAB in the UK use 128 kbit/s joint stereo, which is incapable of providing the same level of audio quality as FM. Speech services usually use 64 kbit/s mono. The only good audio quality service is currently BBC Radio 3, which is usually transmitted at 192 kbit/s in true stereo, but does not sound as good as it does on FM.
The audio is encoded as MPEG 1 Layer 2 (MP2), which is approximately 50% less efficient than MP3, meaning that MP2 requires a 50% higher bit rate to achieve a given level of audio quality than MP3. For example, blind listening tests have shown that MP3 now performs very well at a bit rate of 128 kbit/s, and MP2 would require a bit rate of at least 192 kbit/s to provide the same level of audio quality. Some channels, such as E4 use a shorter picture to reduce bandwidth also.
NTL don't encode / reencode the signals, just play them out, so you should see the same image from all platforms.

EDIT - on the original picture topic, it is all down to bandwidth again. When DVD and compressed encoding first came there was a lot of concern that cartoons, animation, old movies would not convert well, but cleanup, cell realignment and general care in encoding and use of good bandwidth as ensured this has not happened. Just take a look at Bambi, or the Incredibles (or apparantly Japanese Animi) to see for yourself. But DVD can offer up to 8MB of bandwidth for the picture and audio.

[monkey2468]

I noticed the other day that on my dads SKY digi, UKstyle was very pixillated and the sound quality was terrable. It was very over compressed like a 64kbit/s Mp3

[Richardr]

Originally Posted by daniel larusso

Hi, I recently purchased a £30 Digital Freeview box for the 28" widescreen TV in my dining room and have got to say that the picture is stunning and really pin sharp.

Now this has highlighted to me how pixelated and low quality the NTL picture is compared to the Freeview. Surely it should be the other way round? Watching a show like the X Factor or ANT and Dec on the NTL box is like watching a downloaded WMV file and is really blocky (especially when on the audience).

Something doesn't seem right, as the ntl picture for ITV is a straight relay of the Freeview signal, and so they should both look the same.

[MatTman]

something is wrong with Ntl's compression.. its Just bloody horrible, most of the Sci-fi and national geographic channels are terrible.

the old Analogue service was better than this, even terrestrial TV is of much Higher quality than Ntl's tripe.

[SMHarman]

Originally Posted by MatTman

something is wrong with Ntl's compression.. its Just bloody horrible, most of the Sci-fi and national geographic channels are terrible.

the old Analogue service was better than this, even terrestrial TV is of much Higher quality than Ntl's tripe.

Many of the channels you infer above are broadcast at a lower bandwidth than the movie chanels and BBC1, ITV1 etc. You can actually see the pixelation on the E4 logo for example.

Digital is better is not always true, DAB radio uses such low bitrates that it is worse than FM on most channels. Same, but to a lesser extent with DTV as that uses a better compression method.

NTL/TW plans to use a better compression algorithm MPEG4 for broadcasting the next generation of pictures this should also help matters.

[jezza]

I find this all very concerning. I have recently had an NTL engineer over because the quality of the TV picture is (and always has been) really poor, obvious compression artifacts on fast moving pictures, mushy pea football pitches etc. The engineer could do nothing and his supervisor has just called me. He admits that this is down to the high levels of compression they are using as they are trying to get 300 channels down the limited bandwidth available.

Is SKY any better? If so I will move, however will try writing to Simon Duffy first as a matter of principal.

The worrying thing is that these wonderful new digital TV and Radio services are being pushed on the unsuspecting public as the ultimate in picture and sound quality, and most people just sheepishly accept what they are told without question. Meanwhile the government is busy rubbing its hands at the thought of all of the lovely money it is going to make when it forces analogue to close down and sells of the spare bandwidth - leaving the poor consumer with nothing but 1,000s of channels of digital mush - effectively taking us back 20-30 years in terms of transmission quality.

Is it only me or is any one else concerned by this? Should the broadcasters not have some obligation to provide content of a minimum technical quality? Is there any organised pressure group to campaign for this?

As for HDTV, I can't imagine what they will do to that. 720p at 8mbps anyone?

[SMHarman]

NTL do not re-encode, they just broadcast so the same signal is recieved on your NTL, SKY and Freeview box. The hardware in the box may slightly impact the decoding quality, but it is principally bandwidth. Football is one of those things that DTV was not going to improve, too much differing motion and without high bandwidth, which it does not get you get the problems you detail.
You should find that BBC1/2 give very good pictures, as the BBC use more bandwidth on these channels, but bandwidth costs and as a result channels such as E4 use less.

HDTV will use MP4 compression so should get more image down the same pipe.

[Richardr]

Originally Posted by SMHarman

NTL do not re-encode, they just broadcast so the same signal is recieved on your NTL, SKY and Freeview box.

That is not true.

For most of the Sky owned channels, for example, ntl receive the channels via a direct link from Sky, and encode them themselves.

Having said that, there isn't much of a difference between the picture one gets from Sky and from ntl.

[simpsonsFAN]

Originally Posted by Richardr

That is not true.

Yes it is, nor is it a downside as you seam to be making out.

Originally Posted by Richardr

For most of the Sky owned channels

No, "Most of the sky owned channels" are turned around at MPEG level from other platforms. Only sky one and the sky premium channels get the treatment you describe.

Originally Posted by Richardr

ntl receive the channels via a direct link from Sky, and encode them themselves.

But as the sky premium channels are received by ntl in a totaly uncompressed format (270Mbits/second SDI video), and are then encoded at a bitrate that is higher than the other channels, you achally get a better (bitrate) picture on the sky premium channels on NTL, than you would do with sky.

For more infomation, read this more detailed explination:
http://forum.digitalspy.co.uk/board/...19&postcount=5

-Chris

Originally Posted by Richardr

That is not true.

For most of the Sky owned channels, for example, ntl receive the channels via a direct link from Sky, and encode them themselves.

Having said that, there isn't much of a difference between the picture one gets from Sky and from ntl.

I would beg to differ on that one, the picture quality, I have sky and feel their picture quality better than NTL.

[Lew]

Once again though, this could be due to better quality decoding hardware in the Sky STBs.

Originally Posted by Lew

Once again though, this could be due to better quality decoding hardware in the Sky STBs.

And I would agree

But some people seem to think that the picture is the same picture you eventually get whether you have NTL or SKY, I have had NTL and have SKY now, and can see your explanation as a good one.