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Old August 18th, 2011, 06:21 AM   #1
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Multiple renders, etc

I'm pretty sure I asked here somewhere - but can't find it, about how how many times you can render without noticable loss of quality. The situation I was referring to was simply taking an avi file, putting it on a track, cutting some bits out of it, and rendering the result so it was one continuous file. The answer was that there would be effectively no loss of quality over multiple such renders.

I'm now asking if the same applies if that original track - with the bits cut out but not rendered, now also had colour correction and chromakeying done to it. Would the addition of these FX's to the track change anything as far quality goes when the track was rendered - and perhaps then rendered again when other stuff was added?

The reason I ask is that I am trying to work out a post pro work flow for a four camera project, that initially has CC and CK done on every track, and then has CK back images with FX's applied to them, graphics, track motion, etc added. While my computer is pretty good, the addition of FX's slow it down, so I'm thinking I will apply the intial CC and CK and get them out of the way through rendering so that they do not slow the show when the additional material is introduced. I'm also assuming that transparency is retained across/through renders.

I could perhaps include the CK back images into this first render but I haven't yet decided what images to use. Doing this would lock me on on that and I don't want to be locked in re that important aesthetic detail at this stage.

I'm also not clear on how to use the multicam feature in this situation either. I've thought perhaps I could mulitcam the rendered CC and CK'd tracks (as above) and add the appropriate back images under the MC track when I have worked out what back images I want and where I want my camera angle changes...
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Old August 18th, 2011, 07:56 AM   #2
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Re: Multiple renders, etc

What format are you rendering to? That makes a BIG difference. With DV - it's a lot. With more highly compressed formats, it's much, much lower.
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Old August 18th, 2011, 08:02 AM   #3
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Re: Multiple renders, etc

Nothing happens in terms of rendering when you only cut sections of video from a clip and render with the same codec setting, if you don't apply effects you are simply copying your rearranged video into a new file and not rendering.

I'm not sure how many times you can re-render video that you applied effects to but effectively what happens is you are compressing video and then re-compressing the compressed video, all this compression leads to quality loss. The solution is to use a professional codec that is virtually loss-less like ProRes for Mac or Cineform for PC, with these codec's you can render as many times are you like*. If you aren't going to render out more that three times you could probably get away with a high bitrate MPEG-2 compression depending on the quality you need the final product to be.
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Old August 18th, 2011, 01:45 PM   #4
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Re: Multiple renders, etc

Hi

As long as the preview window says "no recompression required" then as said before you are just rearranging the file, however few formats support this type of arrangement.

What format are you using? This makes a big difference.

You can use an uncompressed AVI format, this allows you in theory to go on for ever with no loss even if apply effects and transitions, in practice though it might be going through colour space conversions that could lead to some degradation.

All video formats used are lossy, with the exception of uncompressed formats that you can convert to, but it's rare they start out like this and you would need to take that step yourself. Also the same formats vary in how lossy they are depending on the settings used.

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Phil
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Old August 18th, 2011, 02:46 PM   #5
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Re: Multiple renders, etc

Quote:
Originally Posted by Phil Lee View Post
All video formats used are lossy, with the exception of uncompressed formats
Sorry, Phil, but thatís not true. There are two types of compression, lossy and non-lossy. And, yes, there are video codecs that will compress video in a non-lossy way.
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Old August 18th, 2011, 03:21 PM   #6
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Re: Multiple renders, etc

RE format: I have filmed in GS400 & GS500 cameras > to MINIDV tape > downloaded from the cameras to HDD > imported downloaded .avi files into Vegas > begun the editing as described above > am rendering out to .avi - I presume exactly the same format as I began with...
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Old August 18th, 2011, 04:06 PM   #7
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Re: Multiple renders, etc

If you captured as DV and are rendering as DV, you'll be fine.
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Old August 18th, 2011, 04:49 PM   #8
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Re: Multiple renders, etc

Thanks Edward, that's great. I will proceed... :-)
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Old August 19th, 2011, 11:22 AM   #9
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Re: Multiple renders, etc

I'm probably going to regret saying this but ..... since Vegas does not in any way alter the original files but rather it follows a set of instructions to produce the file which is the result of the render, why would it matter how many times you re-render the original project? Its not like you're working on a JPEG stills photo file which can indeed be degraded by multiple edits and saves if done in Photoshop. My understanding is that Vegas behaves rather like RAW stills file editors such as Adobe Lightroom or Capture One and it merely references the original source with a set of instructions but does not change it.

If you were to re-render the result of an earlier render I guess you would be open to degradation but why would you do that rather than simply re-render the original project saved with a new name having applied your new edits of choice?

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Old August 19th, 2011, 11:40 AM   #10
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Re: Multiple renders, etc

Pete, I was assuming and edit, render, then more editing on the new render, render, then more editing on the new render, etc...

For example, you could color correct a clip, render it out, and then edit using the corrected clip. You could apply a stabilizer, render it out, and then edit with the stabilized clip. Some formats can handle this better than others. DV tends to handle it well.

But you are correct - if you're always rendering from the same original project, you're always using the original footage and so there would be no loss because there really is no intermediate renders.
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Old August 19th, 2011, 12:44 PM   #11
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Re: Multiple renders, etc

Quote:
Originally Posted by Peter Riding View Post
If you were to re-render the result of an earlier render I guess you would be open to degradation but why would you do that rather than simply re-render the original project saved with a new name having applied your new edits of choice?

Pete
A good example of when you would do this is if you are running the footage through a cleaner such as Neat Video to take care of noise. I found the best results for doing this is to take the raw footage, apply the Neat Video plugin to clean up the video and at the same time render out to a Cineform avi. Then I do all my edits and FX/CC on the cleaned CF avi.

Running Neat Video in a very aggressive mode can take 10 or more hours to render so that's a process you only want to do once.

-Garrett
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Old August 19th, 2011, 02:49 PM   #12
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Re: Multiple renders, etc

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Originally Posted by Edward Troxel View Post
Pete, I was assuming and edit, render, then more editing on the new render, render, then more editing on the new render, etc...
That is what I was enquiring about...not constantly returning to the original project...
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Old August 19th, 2011, 09:33 PM   #13
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Re: Multiple renders, etc

interesting thread....

i'm also interested in reading other peoples work-flows when it comes to 'render free' codecs (eg, dv, hdv, mxf, avchd, etc).

most of my work is short form doco and my general method is to first convert any 'odd' formats (mov, etc) to mxf (for ease of editing on tl), and then go through multiple (clean, ie. NO fx, cc'ing, etc.,) 'version edits' each of which is render to a new file (without the need for recompressing). when i finally have a client approved version i can then do what needs to be done in the way of fx, cc'ing etc.,

obviously at this point if i render out to a new file it will be re-compressed. (i usually do a mts just for 'back-up). but obviously at this point i render to clients specs, eg. dvd, mp4, whatever direct from tl.

i have yet to 'see' any difference between original footage and final render using this method.
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Old August 20th, 2011, 01:52 AM   #14
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Re: Multiple renders, etc

So...is it correct that transparency cannot be rendered? I applied a chroma key and rendered without a background image...but can't see through the render...

Have I missed a step, or is it not possible?
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Old August 20th, 2011, 02:01 AM   #15
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Re: Multiple renders, etc

you can render transparency to a codec that has an alpha channel: mov, huffyuv, and others.

big files usually

wait a minute.... you rendered c'key WITHOUT a background!? what we're you expecting to see? a transparency grid like photoshop?
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