YUV format and DC component precision in VCD and SVCD

[cosmin]

Hi,

Is the YUV format always 4:2:0 in MPEG-1, or is it just a limitation of TMPGEnc (which doesn't let me select anything else)? Even if, for instance, I do not wish to make the MPEG-1 stream VCD compliant, 4:2:0 is the only option that I have, at least in TMPGEnc.

I am surprised that 4:2:0 is locked even in the DVD-NTSC template settings, while AFAIK NTSC uses 4:1:1 and only PAL uses 4:2:0. How come that not even 4:2:2 is available? (and worse, when 4:2:0 isn't grayed out, it is still the only option available when making a MPEG-2 stream...)

My other question is about the DC component precision. I know it must be 8 in MPEG-1, and it can be 8, 9 or 10 in MPEG-2/DVD, but I wanted to be sure it must be 8 in SVCD, too. TMPGEnc locks it to 8, but should I trust its SVCD template?

Best regards,
Cosmin

[EddyH]

4:2:0 is DVD quality - MPG2 at main profile and main level. 4:2:2 is some higher level, either high profile at main, main at high, or high at high. Maybe all three. All the same, 4:2:2 isn't covered by the average MPG2 decoder hardware; you can have your DVD luma in 720x480/576, but your chroma is only going to be in 360x240/288 (which is about as much as SVideo supports anyway).... which is better than VCD where it was 176x120/144... yeah it's locked down in MPG1.

(it would be handy to have 4:2:2 for, e.g, CVD.. oh well)

[adam]

Mpeg1 is limited to a DC of 8 but mpeg2 supports 8,9, or 10. Higher DC is recommended for smooth picture with little movement and lower DC is recommended for fast action, but in either case, higher DC is only recommended when using a bitrate higher than 4mbits, so that pretty much rules out SVCD. For SVCD you should pretty much always use 8, In my opinion, and for VCD well you don't have a choice.

[cosmin]

Thank you, EddyH, and thank you, Adam.

Your answers are really illuminating. I wish to point out that I find it weird that NTSC-DVD uses the YUV 4:2:0, while the NTSC television uses 4:1:1. This means that (1) the DVD chroma is downsampled twice horizontally and vertically, and (2) the TV chroma is downsampled 4 times horizontally. As a result, what we get to see on the TV is something like "4:1:0" (I don't know how to call it, but it is the worst of both worlds: the resulting chroma is downsampled 4 times horizontally and 2 times vertically).

This problem does not exist in PAL, since PAL TV uses 4:2:0.

Cosmin