Semi OT: What is 4:2:2 Mpeg 2 for?

TGS wrote on 1/13/2010, 11:03 PM
I've had TMPGEnc for quite a while, and finally noticed that I could render an mpeg 2 in 4:2:2 color. So after setting it up with my favorite settings, with the only change being that it would render to 4:2:2 color Mpeg 2, instead of the normal mpeg2.
Well the file says it's 4.1GB along with a 113MB ac3. If I bring those into DVD Architect, it says it's 5.2GB and that it will have to re-compress the video.
What happened?
Okay, evidently 4:2:2 Mpeg2 must be used for something special and not DVDs.

Any answers? I expect Bob Farss to answer this one, but I'll listen to anybody that knows.
TIA

Comments

farss wrote on 1/13/2010, 11:14 PM
As far as I know the DVD spec does not support 4:2:2 chroma sampling, not to say that it wouldn't work, just that you've got zero certainty it will always work with any DVD player.
Aside from the more expensive Sony XDCAM cameras that record mpeg-2 4:2:2 at 50Mbps I too am at a bit of a loss to see where one would use it. Vegas should be able to decode it OK as it's the same as what's inside the MXF that Vegas can render and decode.
Maybe players other than the bog standard DVD players support it, dunno really. Most mpeg-2 for end delivery is only 4:2:0 as far as I know, the better chroma sampling is very desirable for acquisition.

Bob.
TGS wrote on 1/14/2010, 12:00 AM
Thanks Bob, It seems to play fine in DVD-A, although I can tell it was harder to load in. I had also tried lowering my bitrate and re-encoding, but the new 3.9GB file still said 5.2 GBs when loaded into DVD-A. Then i was going to try to render a DVD file, by setting it up for a 9GB DVD, but it still said it would re-compress the video. I never bothered re-compressing to see what would happen. I just expected it to end up being 4:2:0 Mpeg 2.
PerroneFord wrote on 1/14/2010, 12:58 AM
It's a codec that can be read by nearly anything that supports the Mpeg2 format, but without the drawbacks of 4:2:0 color subsampling. Would be useful as an archive format if there were space concerns preventing use of something more robust.

I am uncertain if the BluRay spec will support Mpeg2 4:2:2
GlennChan wrote on 1/17/2010, 11:58 AM
I'm not sure if 4:2:2 MPEG2 is supported by DVD players.

I believe the 4:2:2 variation is useful in broadcast situations... for sending high-quality video between a satellite and the ground, etc. Though I'm not 100% sure.
Coursedesign wrote on 1/17/2010, 1:02 PM
4:2:2 MPEG2 has been used by broadcasters for more than 10 years, but I haven't seen a DVD player that can handle it.

Too bad, but I believe we'll see more 4:2:2 with improved consumer displays and more advanced codecs thanks to faster CPUs and DSPs.
GlennChan wrote on 1/17/2010, 8:57 PM
It would make more sense to go to 4:4:4 for delivery, especially if you want to have some sort of wide gamut color system in place.

Chroma subsampling is not a very good compression technique. You can think of this way:
Is it better to:

A- Resize an image smaller by 2X to save space, and then blow it up when it is displayed.
B- Apply heavy JPEG/whatever-style compression to save space.

Option B tends to look better. Basically, chroma subsampling is resizing the 'chroma' part of the image down and then blowing it back up.

---

Chroma subsampling made a lot of sense in analog systems because you couldn't do DCT compression... and then it stuck around in the 4:2:2 SDI standard (the backbone of virtually all broadcast facilities). If there were no legacy systems around, chroma subsampling (and interlacing) probably wouldn't make much sense.

Moving forward, I think the future would be 4:4:4 masters (at worst, on HDCAM SR) and distribution would be some next-generation 4:4:4 format. 4:4:4 as in no chroma subsampling used.

----

If you look at JPEG as it is currently implemented, no chroma subsampling is used except at the lower bitrates (where it is helpful). And JPEG is an old standard for older technology. I think the same concepts will apply in the future.

We don't need faster CPUs and DSPs for 4:4:4 to make sense. It already makes sense.
Spot|DSE wrote on 1/18/2010, 2:35 AM
DVDA will re-compress the 4;2;2 into a 4;2;0 stream.
I believe the reason you see some tools offering the 4:2;2 MPEG option is to match acquisition formats for editing compatibility. It cannot be used for delivery to DVD. It can, however, feed other 4:2:2 devices directly.
I'd agree with Course, you'll see 4:2;2 on displays in the higher end sooner than later, so it may at some point, become an option and perhaps a standard. It was proposed to SMPTE at one time (for delivery).