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CBR or VBR for 10 minute Frame Control job

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kyler boudreau
CBR or VBR for 10 minute Frame Control job
on Sep 16, 2010 at 7:54:36 pm

I guarantee you that someone is going to send an assassin after me for asking this, but please know that I've done a lot of reading about VBR vs. CBR, blah, blah. I think I have a unique question:

Got a ten minute timeline that is currently a 1080i 59.94 ProRes HQ sequence. I'm making a DVD and want to turn on all of the frame controls in Compressor to best quality, and wondering with that whether I should do 2-PASS VBR or CBR and do I really have to limit it to a 7500 bitrate for this short sequence?

It seems logical that CBR would be better from reading many opinions, but I don't know. This 10 minute sequence has everything from talking heads to machine gun fire to explosions.

I realize I could test, but I cued one up last night on my quad-core using qmaster and it said it was going to take like 24 hours to encode. WHAT?! So I'm hoping for some forum wisdom that will help me make the right call for the final edit this weekend.

And i'm just going to pump all of the frame controls to best assuming Compressor will handle things correctly.

THANKS.

_______________________
kyler boudreau
http://www.theatereleven.com
ph.310.425.2231


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Michael Sacci
Re: CBR or VBR for 10 minute Frame Control job
on Sep 16, 2010 at 8:30:45 pm

Most people are finding that down the down conversion before the m2v encoding is the way to go. I have gotten good results both ways.

But for ME CBR is the way to go, I have never seen a VBR match the quality of a high bitrate CBR. So you get 3 benefits, quality, speed and better compatibility of playback.

For DVD-R 7.5 is the max bitrate you want to use (and you need to be using ac3 for the audio)

I have an 8-Core 1st gen and I have never gotten encode times even close to that long, I would say 5-6x realtime is the most.

[kyler boudreau] "And i'm just going to pump all of the frame controls to best assuming Compressor will handle things correctly."
Never assume.


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Rafael Amador
Re: CBR or VBR for 10 minute Frame Control job
on Sep 17, 2010 at 2:25:58 am

Hi Kiler,
In GOPs based formats, as important as the data rate is the number of Key Frames.
Try Open and Short GOPs.


[kyler boudreau] "And i'm just going to pump all of the frame controls to best assuming Compressor will handle things correctly."
This is not always like that. In fact, some times, this can leads to the most disappointing results, after very long rendering times.
Rafael

http://www.nagavideo.com


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Michael Sacci
Re: CBR or VBR for 10 minute Frame Control job
on Sep 17, 2010 at 9:48:10 am

It is almost never recommended on changing the gop size or structure with m2v encoding.


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Rafael Amador
Re: CBR or VBR for 10 minute Frame Control job
on Sep 17, 2010 at 9:59:05 am

Hi Michael,
I think that's another myth.
All the Pro applications that I've tried (Bitvice, CinemaCraft, haven't tried Episode), by default uses Open GOPs.
rafael

http://www.nagavideo.com


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kyler boudreau
Re: CBR or VBR for 10 minute Frame Control job
on Sep 17, 2010 at 4:17:26 pm

Thanks guys.

Rafael: so what frame control settings would you recommend. Cause yeah, I'd rather not wait eight hours once this edit is done only to realize it didn't work. Gotta deliver the complete and final on Monday.

Thanks man!

_______________________
kyler boudreau
http://www.theatereleven.com
ph.310.425.2231


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Rafael Amador
Re: CBR or VBR for 10 minute Frame Control job
on Sep 17, 2010 at 4:47:56 pm

Hi Kyler,
First to say, that I agree with Mihael that for this length film, CVR is OK. But you may try what I said about the Open/Short GOPs.
Normally I've been setting Best for the Resizing filter and Better for the De-interlacer.
You don't need retiming in this job. For certain jobs, BEST, does the worst and Linear (the fastest) does the best.
Anyway I prefer to do those tasks with other applications where you have more control or options..
I de-interlace in FC with FieldsKit and resize with SHAKE (better than any option inside FCS).
The truth is that I almost don't use Compressor.
MPEGs with BitVice, H264 with MPGStreamclip or Handbrake..
rafael

http://www.nagavideo.com


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Alan Okey
Re: CBR or VBR for 10 minute Frame Control job
on Sep 17, 2010 at 4:55:14 pm

"All the Pro applications that I've tried (Bitvice, CinemaCraft, haven't tried Episode), by default uses Open GOPs.
rafael"

Indeed. From the BitVice website:


Adaptive GOP Structure

The structure of each GOP is adjusted according to different measures and statistics from the pre-flight pass. The BitVice does not encode an I-frame or even P-frames where not needed. This is one of the tactics, used in the BitVice concept, to minimize misplacement of valuable bits.


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