Technically, it would be best to render straight from the timeline, applying all transitions, filters and color corrections, directly to MPEG2 and bypass the AVI step altogether.

NTSC DV is sampled in the 4:1:1 colorspace, but MPEG2 is sampled at 4:2:0, and to complicate things, in each line only one color difference channel is stored with half the horizontal resolution. The channel which is stored flips each line, so the ratio is 4:2:0 for one line, 4:0:2 in the next, then 4:2:0 again, and so on. This leads to half the horizontal as well as half the vertical resolution, giving a quarter of the color resolution overall. 4:1:1 DV only has 1/4 the color resolution relative to the luminance resolution to begin with, and 4:2:0 is also 1/4 chroma resolution, but when going from 4:1:1 to 4:2:0 some of the chroma samples don't line up in the conversion and they get lost, consequently, a DVD MPEG2 file encoded from a DV AVI file only has 1/8th or 12.5% of the original color information left.

Transitions, color correction, filters, generated media and titling in Vegas is all done in the RGB colorspace, which is 1:1:1, or more accurately, 4:4:4. So any of these things wouldn't take as big a chroma sampling hit if you rendered directly to MPEG2 from the timeline. The DV footage would still take to the 4:1:1 to 4:2:0 hit and there is nothing you can do to avoid this, but anything that Vegas has generated would go directly from 4:4:4: to 4:2:0 and look much better chroma-wise.

I probably didn't explain it very well, but it's late...

John

You get the extra colorspace from still photos as well. So, to restate John's post a little differently: If all your source material is DV, it doesn't matter if you render to DV first. However, if much or all of your source material is generated by Vegas (e.g., titles), or if you have non-DV video captured through something other than DV pass through, or if you have still photos, then render directly to MPEG-2 and skip the DV render, if you want the best possible quality.

An excellent synopsis, John.

So, to restate John's post a little differently: If all your source material is DV, it doesn't matter if you render to DV first.
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John,
When I read John's post it seems to say that it DOES matter.

John Cline said:

"consequently, a DVD MPEG2 file encoded from a DV AVI file only has 1/8th or 12.5% of the original color information left. "

Am I misinterpreting this?

Regards,
John

John_Cline is right - no mater WHAT DV codec you use - as far as I am concerned it kills quality. Then again I don't start with DV either (and not overly fond of it for many things past one generation - no mater the codec used) and would not suggest using it if adding effects, cgi and text and such ..

Rendering to DV would be the worse thing you can do .... (this is my opinion and others will not agree of course)




BTW, saying rendering to "AVI" means nothing, without saying what codec you use - we I guess are all assuming you mean DV, which may be not correct ..

Based on how well your encoder does color space conversions, there are cases where rendering to first - some types - of AVI (or Quicktime) may improve quality ..

The encoder in Vegas is quite good - but with no scene detection and only 1 matrix to use (as well as a few other things) , as well no I frame placement, it is a bit crippled .. you can do I frame placement (or by hand scene detection) with it by rendering sections - but its a lengthy process. Placing markers at scenes doesnt seem to place an I frame there (correct me if I'm wrong - but when I checked it last , it did not) ..

BUT - on the other hand, if you have DV source material , the VEGAS encoder does a GREAT job FROM the time line (no prerender required) , it is highly optimized for this. Using my laird as way to get SP material in to Vegas - I found VEGAS to encode it very well ..

It also does a very good job at high high bit rates in both speed and quality ..



MOST IMPORTANT thing in MPEG encoding is "great source material" in all respects .. if is BY FAR the most important factor and can make even crappy encoders look good ..

Thanks for the reply,
I usually render to {Video for Windows (.avi} using the NTSC DV template in Vegas 4. Then I render to Main Concept Mpeg 2 using the DVDA NTSC video stream and then the AC3 audio stream and author in DVDA 1.0
The original source material is miniDV from a Vx2000.
Given that it seems that you are recommendeing rendering directly to Mpeg 2 from the timeline.


By the way, the only reason I even started to render to .avi first was to try to reduce the likelihood of "flash frames"..........not that any of us know if it even matters, but my thinking is that if I render to .avi first which takes only a few hours, then sit through two hours plus of video looking for the flash frames I only have to rerender for another couple of hours before I render to Mpeg 2 (assuming there are no new flash frames the second time).
The other alternative is a REALLY long Mpeg 2 render, sitting through two hours plus of video, then another REALLY long re-render to Mpeg 2 if the flash frames appear.

You can see why "flash frames" have been one of my pet peeves.
But if the quality of doing it that way is going to suffer I'll just put in the extra time regardless of "flash frames".

Regards,

John

consequently, a DVD MPEG2 file encoded from a DV AVI file only has 1/8th or 12.5% of the original color information left. "

Right. We're saying the same thing. DV doesn't have as broad a color space, so if your original footage is DV, then it already has less of a color space. Once that is true, rendering to MPEG-2 (or any other format) can't bring back what isn't there. In addition, the Vegas DV encoder is so good, that you can render MANY generations and not detect any difference. Lots of tests have been posted on this forum over the years that prove this. Thus, if you do an extra render (or two) to DV when the original footage was DV, it won't make any difference.

I think the quality overall of the Main Concept encoder is very good. The following article gives a real world example of what others were talking about and shows the shift both in color space numbers and in illustrations once you start compressing how colors get "muddy".

Bottom line, if you use transitions, apply filters, do generated media, and who doesn't, its mostly a academic discussion.

http://www.larryjordan.biz/articles/lj_compress.html

Since I use an external MPEG2 encoder (CinemaCraft), I always have to render to a final DV avi anyway. Plus, I throw that DV avi onto miniDV tape as a backup that I store in a separate place.

I can see how working in DV space (lots of vertical color information, limited horizontal color information) and then going to MPEG2 color space (equal but reduced color information both horizontal and vertical) would result in a the worst of either world (mediocre vertical color resolution, limited horizontal color resolution). I would question, however, whether one could actually notice the difference between my procedure and the alternative on a real-world clip. Anybody have any examples?

cinema craft (any version) does a fairly poor job encoding DV source material and would be about 3 or 4 or so down on my list for this application ..

the diff. you mention is quite noticeable to me .. aliasing , banding, submacro blocking, color, edge detail loss are the first things that jump out at you ..

First of all, it isn't "mostly an academic discussion." Secondly, Larry Jordan's article has a few errors in it. BetaSP is not 4:2:2, it's an analog format, if it were a digital format, the way BetaSP color is sampled would be considered 3:1:1, not 4:2:2.

Assuming you start with 4:4:4 uncompressed video, once you compress it to NTSC 4:1:1 DV or 4:2:0 MPEG2, it now has 1/4 the chroma resolution as compared to the luminance resolution. You have 720 pixels of luminance resolution per line, but only 180 pixels of chrominance resolution.

The problem is going from 4:4:4 to 4:1:1 and then to 4:2:0. The color samples between 4:1:1 and 4:2:0 don't line up, some get tossed out and instead of ending up with 1/4 of the original chroma resolutuion, you end up with 1/8th. Essentially, 720 pixels per line of luminance and 90 pixels of chroma. When you take 4:1:1 DV compressed footage and go to 4:2:0 MPEG2, you have to take this big chroma hit and there is nothing you can do about it.

However, any time Vegas is generating anything that isn't the straight, original DV footage, (i.e. using scanned stills, graphics generated in a paint program, titles, certain filters, etc) it generating it in 4:4:4 color space. Even transitions between two DV sources are done at 4:4:4.

Now if you render directly to MPEG2, then in any of the situations where the material is 4:4:4, the material will only that the 1/4 chroma hit. Only clips which are unmodified DV footage will take the unavoidable 1/8th resolution chroma hit.

If you render your project to DV and then to MPEG2, EVERYTHING will take the 1/8th chroma hit. You can, at least, maintain additional color quality on certain areas of the timeline by going directly to MPEG2.

If you really want/need to use an external MPEG2 encoder, then you should look into frameserving the video out of Vegas into your encoder. (I frameserve into ProCoder.)

John

Starting with a false assumption is rather foolish.

Hint:Its academic since the vast majority using Vegas don't start with 4:4:4 uncompressed video. Dah!

Billy,

Hmmm, and I think that posting in a thread with a limited grasp of the concept is rather foolish. Click Here.

I didn't start with a false assumption.

Most people don't start with 4:4:4 video, but as I said, any generated graphics or uncompressed, scanned photographs or anything that Vegas generates, even if it's a title over DV footage or a transition between two DV clips, is ALL done in the 4:4:4 colorspace on the Vegas timeline. These sections of a project will look better on a DVD if you render from the Vegas timeline directly to MPEG2.

In other words, do NOT render to 4:1:1 DV first and then render to 4:2:0 MPEG2. The unmodified DV footage will look the same in either case, everything else will look worse than it would if you rendered to MPEG2 directly.

John
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Er-followup question if I may (before the fight starts):

I have a 97-minute DV feature. Do the color correction plugin and/or the Curves plugin result in a 4:4:4 operation? Nearly the entire movie has both applied.
.

No, I wouldn't think so since neither of these plugins generate additional chroma resolution, they only modify what's already there.

John

This is getting silly. Geez Cline, first you beat your chest acting like the all knowing Oracle and then when asked a specific question about Vegas you ADMIT you don't know, you simply say "... I wouldn't think so"

Priceless!

For those from Missouri "show me" comes to mind. So here's a challenge for Cline.

Put up two identical clips contained material you think will alter video quality due to changes in color space, render one from the timeline, the other not.

Lets see what differences (if any) we collectively "see".

OK, Billy, the answer is NO, neither the color correction nor curves plugins will generate additional chroma resolution and therefore would not benefit from rendering directly to MPEG2 from the timeline. There, are you satisifed?

I'll GLADLY take your challenge, Billy.

I have posted a .ZIP file on my web site that contains the results of a test I just did. I took a 720x480 4:4:4 graphic, rendered it as a DV file and an MPEG2 file from Vegas. The DV file was rendered using the Vegas DV codec and the MPEG2 file was rendered from Vegas at 8Mbit CBR, quality slider at 31.

I then took the resulting DV file, placed it on the Vegas timeline and rendered it as an 8Mbit CBR MPEG2 file using exactly the same settings as the other MPEG2 file. I took all the results and pasted them side-by-side into Photoshop and generated a test results .BMP file and the results turned out EXACTLY as I expected. It is interesting to note the difference between 4:1:1 and 4:2:0 color sampling. Nevertheless, the uncompressed graphic > DV > MPEG2 is, by far, the worst looking of the bunch. I think even Billy can see this. (Make sure you view the test results image at 100% scaling in your image viewer.)

The .ZIP file contains the test results image file and three 720x480 4:4:4 test images you can put on the Vegas timeline and do the test yourself. (Make sure to set the aspect ratio of the graphic in Vegas to .9091 and not square.)

Get the 477k .ZIP file HERE.

John

This is a warning to anyone considering a flame war on this thread.

If you start it or add to it, you will pay the consequences of carrying on your personal battles in our forums. Simply put, those fights do not belong here, period, and will not be tolerated. We encourage constructive input, for the betterment of all our users. As soon as you take it to a personal level, your presence will no longer be welcome in the Sony Media Software forums.

Thank you.

Nice example, John. One question, did you test an 4:1:1 clip using just Chromablur effect on color space going to 4:2:0?