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Old November 21st, 2007, 12:05 PM   #1
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DV AVI vs. Uncompressed

I keep seeing folks mentioning to render out a timeline to Uncompressed as opposed to rendering out to the NTSC DV AVI. What exactly is the difference besides uncompressed being an astronomical file size? 5:1 if I understand correctly. I understand that uncompressed is...well....uncompressed, but what purpose does it serve to uncompress a format that is originally already compressed? Does it help with a better mpeg2 compression if its "uncompressed"?....and how much wood could a wood chuck chuck..
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Old November 21st, 2007, 12:19 PM   #2
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what purpose does it serve to uncompress a format that is originally already compressed?
The purpose is to avoid compressing it *again*.
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Old November 21st, 2007, 12:22 PM   #3
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Say I capture an hour of DV footage....it's 13 gig....if I render it out to AVI...its still 13 gig...so its not compressing it again. Am I just completely missing something here?
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Old November 21st, 2007, 12:24 PM   #4
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IMHO uncompressed is madness, madness I say.

Possible exception is when going back and forth with after effects or other external graphics.

When I'm done I render to MPEG2 from the timeline - you don't get any better with generational loss than that, even with uncompressed. DV is darn good for an intermediate format for standard def, almost always good enough.

Another alternative is Cineform - usually we just think about it as an intermediate for HD, but it can be used with SD as well.

Lessee'... if "Content is King", then workflow is an usurper of the throne, who, if you're not careful, will poison the king, leading to a lengthy convalescense and poor governance...
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Old November 21st, 2007, 12:29 PM   #5
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Say I capture an hour of DV footage....it's 13 gig....if I render it out to AVI...its still 13 gig...so its not compressing it again. Am I just completely missing something here?
The file size is irrelevant. If you changed a frame (e.g. major color grading), it will be re-compressed, and that may cause compression artifacts that an uncompressed format would not have had. (Generally, DV-AVI is a light-enough codec that the generational loss is acceptable for most work.)
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Old November 21st, 2007, 12:33 PM   #6
 
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DV is very much like the JPEG photo format. Everytime you view it, it is uncompressed for viewing. Every time you save it, it is recompressed for saving. If you've made no changes, don't resave it. If you have made edits and it must be resaved, you'll suffer a generational loss in the recompression.
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Old November 21st, 2007, 12:37 PM   #7
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I don't deal with uncompressed files so the following is based on what I've read here and elsewhere.
You want uncompressed so that, no matter what you do to it (color correction, adding FX, etc.), the image quality is degraded as little as possible.

Here's an example for you.
Bring a copy of an image from your digital camera into Photoshop and save it as a JPEG without doing anything to it. Repeat this process 7 or 8 times. Compare the multiple saved one to the original and you should see a loss in picture quality.
Now repeat this process but save it as a PNG each time. With PNG being a lossless format, the loss in image quality should be negligble.
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Old November 21st, 2007, 12:56 PM   #8
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OK...So in your professional opinions...I have a documentary project that has over 70 timelines and is 90 mins long. I would say that 90 percent of it has some type of color correction filters applied to various clips. What I had been doing is rendering that project to DV AVI and then rendering that avi file to my mpeg2 file. It seemed easier to do it that way, simply because it took 2 hours to render to the avi and another 2 hours to mpeg2 so it basically knocked off 2-4 hours of render time if I was to just render the project directly to mpeg2. I know...you cant rush quality!! So,...should I render the project out to uncompressed or should I render directly to mpeg2? Im thinking either will end in the same results, but If I have the master uncompressed, I can play with my mpeg2 settings alot easier after that. This whole explanation would explain why there is one perticular interview that is HEAVY on the color correction more so than the others, and looks like complete junk!
By the way,...this piece actually won Best Documentary at the Colony Film festival this past weekend. It looked great on the big screen, but on the smaller screen, the bad stuff really comes out!
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Old November 21st, 2007, 01:11 PM   #9
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So, should I render the project out to uncompressed or should I render directly to mpeg2?
You have two separate questions. To answer the second, lesser one: if you knew the mpeg2 settings, it would be fastest to encode directly to mpeg2. Plus, it would be equal in quality to using uncompressed as an intermediary.

The more pressing question is based on your desire to get a full render of the entire project that you can use to play with different mpeg2 encoder settings. I assume you desire this because your NLE doesn't support scripting so that you could encode just several dozen selected clips.

Uncompressed will have higher quality; that's given, but many people can't tell the difference in analyzing stills, let alone moving images. In any case, the difference will not be as big as, say, source material codec differences. There are several orders of magnitude between uncompressed 4:4:4 and DV-AVI as source material.
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Old November 21st, 2007, 01:36 PM   #10
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I dont know my mpeg2 setting quite yet...thats my whole objective. I am trying to perfect it before I give the final project to the manufacturer for pressing.
I like to render a full project out, just to have the master print when I am done with my editing. From that master print, I toy with the mpeg2 rates, try to get that optimal size (etc, etc) that I need, slap it on a disc, verify it...by watching the whole thing....over and over ,...and if something is screwed up in the mix,...go back and edit, and then render back out to avi and start all over.
Im on Vegas 7, but I dont really use alot of scripting! Actually I dont use any...that I am aware of. I think the only scripting I have ever done is image sequencing. Never really learned the finer points of it...my editing skills and proficency levels are pretty primitive.
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Old November 21st, 2007, 01:57 PM   #11
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I dont know my mpeg2 setting quite yet...thats my whole objective. I am trying to perfect it before I give the final project to the manufacturer for pressing.
Sounds like you need a bitrate calculator.
Here's a link (to a zipped file) to the one that I use.
Enter in the type of DVD (single or dual layer, the type of audio file (AC-3 default for Vegas default is 192 Kb/s), the program length and whether you want CBR (Constant Bit Rate) or VBR (Variable Bit Rate).
The usual recommendation is to not exced 8 MB for video but, based on suggestions from Spot (Douglas Spotted Eagle), I've bumped this up to 9 MB. As long as you stick to good quality media (Taiyo Yuden or Verbatim), you should be OK.

When your done with your Vegas project, render to MPEG -2 & AC-3 separately.
Make sure both files have the same surname (eg. MyVideo.mpg & MyVideo.ac3).
Select the "DVD Architect NTSC video stream" as the render template.
then click "Custom" and then the "Video" tab.
Click either CBR or VBR and enter the settings you got from the bitrate calculator.
This can be saved as a preset in the box at the top of this same tab.
Give it a name that makes sense to you and click the "Save" icon (looks like a floppy disc).

BTW, Vol. 1 #7 of Edward Troxel's excellent newsletters is devoted to DVD authoring and I recommend reading it.
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Old November 21st, 2007, 01:59 PM   #12
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Unless one works in a highly ineffective manner like add an effect, then save, then reload the saved project, add another effect, save, then reload the saved project, add another effect, save... so unless one does that, uncompressed format should not be needed.

Obviously, making effects in 8-bit transport colorspace is not precise enough, so an NLE should uncompress behind the scenes into something with 10 or 12 bit per component, perform needed effects, then recompress back. Also, it should not recompress portions that have not been modified if the target format is the same as the source format.

Another reason for uncompressed format or for frame-by-frame compression like MJPEG/DV is lower requirements for computing power.

With a powerful computer and with good NLE I don't see any reason for explicit conversion into uncompressed format. Do I not see something that everyone else sees?
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Old November 21st, 2007, 02:07 PM   #13
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Michael,
I'm still working in the same original timelines with all the original assets..they have never been rendered out and then added to if that is what you are refering to, but as far as adding,...saving,...adding & saving,...I've been doing that for 2 years now on this project. But like I said,..its still all the original raw assets.
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Old November 21st, 2007, 02:09 PM   #14
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DV compression is 5:1 DCT-based, and the chroma format is 4:1:1 (chroma subsampled 4x horizontally)... the effective bandwidth reduction is actually more than 5X. It's something like 10X bandwidth/datarate reduction. Uncompressed 4:4:4 files are really big. (There are also uncompressed 4:2:2 files... e.g. no DCT-based or wavelet-based compression, but the chroma has been reduced 2X horizontally).
You might want to render to a cineform intermediate since it's more practical and you're not really losing quality. It's good to have an intermediate render sticking around in case you need to make additional outputs (e.g. web streaming, or you screwed up the MPEG-2 render, etc.).

2- Audio is calculated separately. In this case, the audio is uncompressed so it stays the same size.
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Old November 21st, 2007, 02:29 PM   #15
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Originally Posted by Mike Kujbida View Post
...Here's an example for you.
Bring a copy of an image from your digital camera into Photoshop and save it as a JPEG without doing anything to it. Repeat this process 7 or 8 times. Compare the multiple saved one to the original and you should see a loss in picture quality...
I'll certainly agree with Mike on that, however...

In jpg you have that quality setting (compression setting) that will determine how lossy the compression is. With minimum compression I think jpg uses run-length-encoding (RLE), which is not lossy.

More importantly, we're talking about adding one generation of DV, not seven or eight.

Ya' know, this is one of those questions that's very difficult to answer, "How good is good enough?" I remember doing tests back quite a few years ago and only seeing visible artifacts after more than 10 generations of DV. But memory fades... Maybe I'll repeat that test this weekend.

And this is perhaps the real answer - test and see what works for you in your workflow, with your content, your desired output. And do check out cineform at standard def! It's a great codec and far more economical than uncompressed.

It is far too easy to say "uncompressed is best". Well, it is, however, we also have to deal with several other factors (time, money, storage) in a professional workflow. Back in my days in broadcasting, we used to ask "will they see it at home?" If not, it didn't matter.

May I also suggest that you prepare a 5-minute version of your project for MPEG2 encoding tests. Include representative scenes as to color and action, and you can do a lot of testing in a hurry!
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