[jimmyboy]

[fernandez]

Have a look at these

http://www.bbc.co.uk/rd/pubs/papers/...paper_14.shtml

http://www.chiariglione.org/mpeg/sta...g-2/mpeg-2.htm

The basic explanation is

"4:2:2 means the chrominance is horizontally subsampled by a factor of two ... signal at the coder prior to transmission and re-inserting it at the decoder. ..."

Suffice it to say that 4:2:2 transmissions can only be decoded by specialist receivers.
Standard transmissions are 4:2:0

[Didds]

Live feeds that haven't been edited and aren't for the viewing public. Hence the reason why they are encrypted and can only be decoded by specialist receivers (£600 plus).

[remlap]

Originally Posted by Didds

Live feeds that haven't been edited and aren't for the viewing public. Hence the reason why they are encrypted and can only be decoded by specialist receivers (£600 plus).

4:2:2 IS NOT ENCRYPTION, 4:2:2 does NOT mean its unedited.

And no where costs £600 +

[Didds]

Originally Posted by remlap

4:2:2 IS NOT ENCRYPTION, 4:2:2 does NOT mean its unedited.

And no where costs £600 +

Lol. I stand corrected. Are most 4.2.2 transmissions not encrypted ?
The £600 came from the price for a Qualitv receiver, which I thought was the cheapest receiver you could but to receive 4.2.2 transmissions !!

[remlap]

No-Way of knowing what chroma is in use for encrypted feeds but I assume for broadcast it would be 4:2:2 on 7e atleast.

Quali TV boxes go for £60 second hand of ebay now, and a PCI satellite card costs £30 for a computer.

[Didds]

Originally Posted by remlap

No-Way of knowing what chroma is in use for encrypted feeds but I assume for broadcast it would be 4:2:2 on 7e atleast.

Quali TV boxes go for £60 second hand of ebay now, and a PCI satellite card costs £30 for a computer.

Thanks for the info. I didn't realise Quali tv boxes were so cheap now.
Off to ebay then.

[bazovcarlisle]

i would recommend getting the skystar 2 pci card to decode these feeds as the tuner in the quali box are useless

[Stephen Neal]

To answer the OP's original question.

4:2:2 is the standard system used to sample broadcast video for distribution around a broadcast centre. The 4 refers to the sampling rate that is used for the luminance (Y) i.e. the brightness signal, the 2:2 refers to the sampling frequency used for the two colour difference signals (R-Y/Cr and B-Y/Cb) i.e. the colour/chrominance.

This means that the colour information is sampled at half the resolution horizontally as the brightness - which is fine for most things (though it can cause issues with chroma-keying where you need high resolution colour information) as the eye/brain is less sensitive to colour than brightness. However vertically, in 4:2:2, the resolution is the same for both the luminance and chrominance. This has advantages in broadcast applications - particularly in interlaced systems where the vertical resolution is effectively halved on moving information where there is movement between the two fields within a frame... (*) If 8 bit sampling is used then 4:2:2 subsampling from 4:4:4 reduces the number of bits required to code each "pixel" from 32 to 16.

However for DVD, HD-DVD, BluRay and both SD and HD broadcasts to the home, 4:2:0 is used. This reduces the chrominance resolution vertically as well, by sending just one colour signal - either R-Y or B-Y for each line, and alternating them. (Incidentally the French SECAM colour system did this as well). This means that the vertical chroma resolution is now halved as well giving a balanced horizontal and vertical chroma resolution, and also requiring less space to carry - as now only 12 bits per "pixel" are required - as for every 4 luminance samples (in a 2x2 array) there is only one R-Y and one B-Y sample...

What has this got to do with satellite feeds?

Well 4:2:2 satellite links, using a different MPEG2 Profile to 4:2:0 direct to home links, are used by broadcasters for their high quality links from outside broadcast locations back to their network control areas. These links are likely to be at a higher data rate - say 24-34Mbs rather than the 3-6Mbs used to broadcast to us - and the 4:2:2 video is higher quality, and will survive around a broadcast area in quality for longer.

4:2:2 MPEG2 is not usually decodable by domestic SD satellite receivers - hence it appears to be encrypted - but in fact it isn't always. Some HD MPEG2 receivers can decode SD 4:2:2 as can most PCs with DVB-S cards and the right MPEG2 software codec (with 4:2:2 support - like the Elecard ones?)

Bottom line - 4:2:2 at a high data rate is usually used by broadcasters as it is higher quality - and thus when the signal is recompressed to broadcast to us the quality is higher than if 4:2:0 were used.

(News broadcasts may often use 4:2:0 at lower rates though)

(*) In interlaced systems the resolution of a 50Hz SD the luminance signal can drop from 720x576 to 720x288 on fast moving information, and in 4:2:2 you get a resulting 360x288 chrominance signal. Worst case scenario with 4:2:0 is that you get 360x144 resolution chroma on interlaced fast moving content, which is why 4:2:2 is used within broadcast centres. This is because a 720x576/50i signal behaves like a 720x288/50p signal on fast moving information - the trade-off with any interlaced system is that the vertical resolution and motion resolution are not independent.

[Chris Muriel]

That's a great synopsis, Steve.
I just want to add, for anyone buying a secondhand QualiTV box, please check the electrolytics around the power supply area as these fail over time; if you don't have the techncial knowledge, have someone who does do this. I would be inclined to swap all the power supply electrolytics for higher temperature rated ones before putting the box into use.
Thread in USA Satforums section (of which I am a longstanding member) under "Other Receivers" has more about this :
http://forums.satforums.com/SatForum...p?msg=14244.18

Chris Muriel, Manchester

[Neil Watson]

Very good post explaining the differences between 4:2:2, 4:2:0, etc.

Without going too far off topic, does this apply to HDMI transmissions between devices? Just wondered as I have those options as well as RGB(0-255) and RGB(16-255) on my DVD recorder and when left to negotiate over HDMI with my TV, it defaults to 4:2:2.