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VBR vs CBR (mpeg2 vs mpeg2-DVD)

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VBR vs CBR (mpeg2 vs mpeg2-DVD)
by Marc Thomas on Apr 27, 2011 at 11:47:58 pm

I have a short film (11 minutes long) that I've color corrected and added titles in AE and rendered out for Premiere Pro:

When I export from Premiere Pro as mpeg2-DVD, VBR 2-pass (high quality settings)... my titles look good, but CBR (8mbs) makes my titles look jagged with "combing" effects.

When I export from Premiere Pro as mpeg2... both VBR 2-pass and CBR (8mbs) look good.

If you take the titles out of the equation... comparing the two CBR's... the rest of the footage looks slightly better with mpeg2-DVD.

I've read that with shorter run-times, you should use CBR... if that's the case, then I'd go with mpeg2 (because of the titles).

But do you know why I saw a drastic difference with the titles? What's going on here?

Thanks,

Marc

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Re: VBR vs CBR (mpeg2 vs mpeg2-DVD)
by Tim Kolb on Apr 28, 2011 at 12:01:04 am

CBR or constant bitrate encoding doesn't adjust the bitrate when high detail situations come up...or adjust it when there is a static shot and a highly reduced bitrate would be fine.

If you didn't inadvertently get an interlace/progressive setting wrong in the CBR version, I'd guess the titles are highly detailed? ...maybe animated somehow?

TimK,
Director, Consultant
Kolb Productions,

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Re: VBR vs CBR (mpeg2 vs mpeg2-DVD)
by Marc Thomas on Apr 28, 2011 at 2:08:05 am

Thanks Tim,

Yes they're animated... But why is one CBR better than the other?

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Re: VBR vs CBR (mpeg2 vs mpeg2-DVD)
by Tim Kolb on Apr 28, 2011 at 2:14:22 am

Well...that's why I'm saying you should try to backtrack and check the interlacing setting. The DVD settings likely default to interlaced.

TimK,
Director, Consultant
Kolb Productions,

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Re: VBR vs CBR (mpeg2 vs mpeg2-DVD)
by Tim Kolb on Apr 28, 2011 at 3:53:56 am

Yeah...that's why I want you to double check the interlace setting as the DVD preset is likely defaulting to interlace and you may not want that if you are using progressive source material.

TimK,
Director, Consultant
Kolb Productions,

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Re: VBR vs CBR (mpeg2 vs mpeg2-DVD)
by Jeff Greenberg on Apr 28, 2011 at 4:19:20 am

Well, MPEG2 compression was designed to fool the eye on video (the way the jpeg does with stills.)

But titles? Especially moving titles? Tim's dead on - it's the extra details.

WIth VBR, the encoding is 'robbing peter to pay paul' and actually peaking higher than the average bitrate. Which is what VBR is meant to do.

Althought at that high of a bitrate, I'm surprised theres a problem.

Best,

Jeff G

Apple Master Trainer | Avid Cert. Instructor DS/MC | Adobe Cert. Instructor
------------
You should follow me (filmgeek) on twitter. I promise to be nice.
Come See me speak at NAB!
Compressor Essentials from Lynda.com
(older but still good) Marquee, Media Composer (3.5) and Basic/Advanced Color DVDs (1.0) from Vasst.com
Contact me through my Website

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Re: VBR vs CBR (mpeg2 vs mpeg2-DVD)
by Marc Thomas on Apr 28, 2011 at 5:11:45 am

Thanks guys!

Tim: It is interlaced material that I'm working with... and both versions have the exact same settings except that one is mpeg2 CBR and the other is mpeg2-dvd CBR. Both interlaced... one has TERRIBLE titles. I don't get it?

Jeff: I'm not having problems with the VBR versions (both look good). I'm just having problems with the mpeg2-dvd version of CBR... which is confusing me.

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Re: VBR vs CBR (mpeg2 vs mpeg2-DVD)
by Ann Bens on Apr 28, 2011 at 10:06:57 am

If its for Premiere Pro i would use neither.
You want an intermediate file not a compressed one like mpeg, as you are going to export again.
Use uncompressed or Lagarith or even Cinefom.

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Re: VBR vs CBR (mpeg2 vs mpeg2-DVD)
by Tim Kolb on Apr 28, 2011 at 8:35:52 pm

...Jeff's right on the data rate...it's rather massive for a DVD file.

If it's all exactly the same...(frame size and pixel aspect as well?), it may be a bug in the software.

I still suspect there may be a very nuanced differnce in there somewhere...

(Sorry for the double post...I didn't see my initial response post, so I tried again.)

TimK,
Director, Consultant
Kolb Productions,

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Re: VBR vs CBR (mpeg2 vs mpeg2-DVD)
by Ivan M. Semeniuk on May 6, 2011 at 9:15:48 am

MPEG2-DVD is a subset of MPEG-2 and has fewer options available. What were your MPEG-2 settings for the parameters that do not appear under MPEG2-DVD?

I just encoded a test clip to see if I could replicate the issue. The resulting videos were nearly identical with only faint differences between them.

- What version of Pr/AME are you using?
- How did you create and animate the credits (Title Designer with motion effect, imported file, rolling/crawling text, other)?
- Is there another clip playing under the credits or does the text appear against a transparent background?

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Re: VBR vs CBR (mpeg2 vs mpeg2-DVD)
by Jeff Greenberg on May 7, 2011 at 11:40:08 pm

Here's the deal: if you're VBR, it's stealing data from somewhere else to handle the hard edges in the graphics.
But CBR? It can't deal with the data.

Now, for a serious question: are we just academically trying to drill down to an answer?

Best,

Jeff G

Apple Master Trainer | Avid Cert. Instructor DS/MC | Adobe Cert. Instructor
------------
You should follow me (filmgeek) on twitter. I promise to be nice.
Come See me speak at NAB!
Compressor Essentials from Lynda.com
(older but still good) Marquee, Media Composer (3.5) and Basic/Advanced Color DVDs (1.0) from Vasst.com
Contact me through my Website

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