Does Re-Render Reduce Quality?

[Steve Rhoden]

Re-rendering reduces quality yes, but for it to be visible to the
naked eye, it would have to be re-rendered many numerous times over.
So don’t worry about it, You aint gonna see any difference whether
second or third render.

“Should the settings be the same for the first render as well as the final render?”
Yes it should.

Steve Rhoden
(Cow Leader)
Film Editor & Compositor.
Filmex Creative Media.
https://www.facebook.com/FilmexCreativeMedia
1-876-832-4956

[John Rofrano]

[Jerry Hart] “I want to edit in segments of about 5-10 minutes each so the timeline doesn’t get too long to manage. If I render each segment separately and then assemble the rendered files together on the timeline for the final render, will the second render reduce the quality of the project?”

It can but it doesn’t have to. It depends on which codec you use to do your intermediate renders. Some codecs are “lossy” and will loose quality on every render. Some codecs are “lossless” and will not loose any quality when rendered. Some codec are “visually-lossless, or “near-lossless” and while they do loose some quality, your eyes can’t detect it under normal circumstances.

So you can render your sections to a lossless codec like Huffyuv or Lagarith. You can use a digital intermediary codec that is near-lossless like CineForm or Avid DNxHD. Or you can simply render to a lossy codec at a high bit-rate like Sony MXF @ 35Mbps and I bet your eyes won’t see any loss in quality. I would recommend you do your section renders to Sony MXF. I think you will be pleasantly surprised how well the quality holds up when you do your final render to Blu-ray.

~jr

http://www.johnrofrano.com
http://www.vasst.com

[Stephen Mann]

Well, technically, rendering has practically no effect on quality because rendered formats are all I-frames, like AVI files, and not compressed. (Since I’m nit-picking, AVI files are compressed slightly in the camera, about 5%, but Vegas does not recompress AVI).

Encoded formats, on the other hand, like h.264 or QT will suffer generational loss quickly because you are recompressing already compressed data.

But, what you probably want to do is to use embedded veg files. This way there is no recompression.

Steve Mann
MannMade Digital Video
http://www.mmdv.com

[John Rofrano]

[Stephen Mann] “Well, technically, rendering has practically no effect on quality because rendered formats are all I-frames, like AVI files, and not compressed.”

Jerry, Just to be clear…

Steve is referring to the fact that the term “rendering” only applies to apply the effects, etc. to a video and then once rendered in memory, it is “encoded” to a particular format on disk. I did not make that distinction because Vegas Pro calls the whole process “rendering” and I believe that’s what you meant. Vegas never talks about encoding as a separate thing so I thought it might be confusing to introduce it in this conversation but Steve is right about “rendering” vs “encoding”. He did qualify his answer with the word “technically” but I thought it was worth elaboration.

I would also like to point out that AVI was not the best analogy because AVI files are not always I-Frames. The encoding is determined by the codec. You can put H.264, or DivX, or Xvid in a AVI file and it is not all I-Frames. AVI is just a container that has no bearing on how the video is encoded. It is interesting to note that Vegas doesn’t handle AVI files that are not all I-Frames so, in general, AVI files should only contain codecs that use all I-Frames but people don’t always follow this rule.

[Stephen Mann] “Encoded formats, on the other hand, like h.264 or QT will suffer generational loss quickly because you are recompressing already compressed data.”

Well… while H.264 is an encoded format, QT (QuickTime) is not. It’s a container just like AVI and you can certainly have all I-Frames in a QuickTime file and render QT files with no loss. This is why I was very careful to discuss codecs in my answer because it’s the codec that determines if the encode will be lossy or not. It has nothing to do with AVI or QT.

Also not all encoding uses lossy compression. You can compress a video 1000 times with Lagarith and you will get the exact same video every time because Lagarith uses lossless compression much like a ZIP file which always gives you back the exact same files regardless of how many times you ZIP them. So recompressing already compressed data is OK if you use lossless compression.

[Stephen Mann] “But, what you probably want to do is to use embedded veg files. This way there is no recompression.”

I agree with Steve 100%. If you are using Vegas Pro and not Movie Studio then use nested projects. Just make a master project and drop all of your other projects into it to assemble the final video and there will be no re-encoding at all. (…now why didn’t I think of that) 😉

~jr

http://www.johnrofrano.com
http://www.vasst.com

[Jerry Hart]

My original footage was shot with Lumix Gh3 – .mov I-Frame 24p 1920×1080 at 72Mbps. I’m using Vegas Pro 12.

I didn’t know about nested projects and that I could assemble .veg files into a master. How do I load separate .veg files onto the timeline?

Also, once I get the master assembled, what render choice is best for the best quality Blu-ray?

[Steve Rhoden]

How do I load separate .veg files onto the timeline?
You can simply drop your .veg files on the timeline as you would
do with any video clip (Event).

Steve Rhoden
(Cow Leader)
Film Editor & Compositor.
Filmex Creative Media.
https://www.facebook.com/FilmexCreativeMedia
1-876-832-4956

[Stephen Mann]

I took the long way to get to the point. Thanks for correcting my inconsistencies. Shortly after I posted that I thought of DivX in an AVI container – talk about a mess that Vegas doesn’t get along with well.

Steve Mann
MannMade Digital Video
http://www.mmdv.com

[John Rofrano]

Yea, instead of selecting a video file, you select the .veg project file and when you drop it onto the timeline it behaves like any other piece of media. You can trim it, crop it, and add FX to it and even right-click and open it in another instance of Vegas Pro and edit it and return to the master project will all of your edits updated. It’s really an awesome features for working in sections.

~jr

http://www.johnrofrano.com
http://www.vasst.com

[John Rofrano]

[Stephen Mann] ” Shortly after I posted that I thought of DivX in an AVI container – talk about a mess that Vegas doesn’t get along with well.”

Yea, I understood what you meant and this is exactly why Vegas doesn’t handle DivX in an AVI container. It’s expecting a codec that uses intraframe compression and when it finds one that uses interframe compression it will read it but you get all sorts of strange artifacts and it never renders correctly. So you are correct, AVI files should only contain intraframe codecs for best compatibility.

~jr

http://www.johnrofrano.com
http://www.vasst.com