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Old December 1st, 2003, 03:45 PM   #1
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authoring questions (ac3, bitrate)

I have already read not to use a bitrate over 8000 since
the surfaces of consumer DVDs aren't reflective enough, but
since I am having the DVD-R glass mastered, could I not
use the highest possible bitrate, since the final would be
on a regular mastered DVD? (The movie is only 15 minutes long)
Would that work without the skipping/focusing problems?


Also, would I be safe in using a single ac3 track? If the
viewer only has 2.0 stereo, then they hear just those two
channels, and if they are using 5.1, then they hear all channels ?
Does this make sense?
I know pros use two separate tracks, but I have no idea how to
lay something like this out in my mastering software
(Vegas+DVD)....as far as the ability to switch between tracks.

Thanks for your help!


,Frank
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Old December 2nd, 2003, 06:36 PM   #2
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Yes you can max out the datarate if you are getting it pressed. Replicate from DLT if you can. If not use a dvd-r(A), or give the rep house a HD and see if they will author. If not then dvd-r(G) it is. Yes you can use a single AC3 stream but the 'pro' 5.1 mixes are done so they downmix to 2.0 if played on a stereo setup.

Jake
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Old December 2nd, 2003, 06:56 PM   #3
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All system that support dolby digital playback should be able
to downconvert it to stereo. But I can't imagine this isn't possible
in Vegas as well. What happens if you just save it as a stereo
WAV/PCM/AC3 file?

I would be a bit reluctant to go to the maximum on bitrate. I
don't think I've ever seen a DVD that actually pushes the
maximum boundary. Yes it should work, but I wouldn't tempt
faith like that. A lot of people have very cheap players with
the cheapest components available.
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Old December 2nd, 2003, 07:20 PM   #4
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Man I've loads of dvd's that are 10 Mbps CBR. Matter of fact I've got Gangs of NY on right now and it is.

The main problem as far as replication goes is if you have a spike at a layer switch then that can cause issues but other than that you can raise it up. It's one of the advantages of going to replication,

Jake
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Old December 2nd, 2003, 07:34 PM   #5
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Okay Jake. I'll keep an better eye on that bitrate meter on my
DVD player when playing those movies. I've probably been wrong
about that then.
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Old December 2nd, 2003, 07:39 PM   #6
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Not wrong as many do use VBR as you'd expect but there also quite afew who use quite a high CBR datarate,

Jake
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Old December 2nd, 2003, 09:56 PM   #7
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Jake: What's the difference between dvd-r(a) and dvd-r(g)?
Sorry for sounding ignorant - I am brand new to DVD authoring. :-)

A lot of mastering houses work from DLT, but the one I am
considering using (TripleDisc - Fredricksburg, VA), says that
they are now only taking dvd-r, and they say a lot of people
are doing that now because the extra expenses of going
from DLT don't outweigh the quality. This make sense to
you guys?


I guess I may stay safe and keep it at 8, since I have done tests on that and it looks fine.

Would just a 8 Mbps CBR be sufficient? I wouldn't have to use
VBR, would I? (The short is around 15 minutes, btw.)


Thanks a lot for all the help!

,Frank
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Old December 3rd, 2003, 04:08 AM   #8
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Well dvd-r(A) is authoring media and you need an authoring drive to write it, dvd-r(G) is general media which is the 'normal' media.

www.dvddemystified.com/dvdfaq.html 4.3.2 I think for more on both of those.

Wow thats just amazing. Everytime I hear of a rep house that says that I just can't beleive it. It's only the 3rd time but I just hope it's a sales person that says it and not a tech guy or they aren't the rep house and outsource the job.....

"the quality."

We'll it isn't so much quality(depending on how you define quality), it's a compatibility issue really. And when a rep house advises against the 'standard' then is just strange to me.... Make sure you send more than one dvd-r, but that said it doesn't sound like that rep house would run it through any major tests if it wants dvd-r over DLT.

Well it's kinda down to you CBR or VBR. I'm not sure what control over VBR you have with your encoder. If you can set the max and min bitrate then you could run it through a 2-pass VBR encode. It's only 15 mins so shouldn't take too long and you can compare how things look with the various settings,

Jake
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Old December 3rd, 2003, 05:01 AM   #9
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weird when i had some stuff replicated for a festival recently... i just plugged in my external HD and gave them the image of the dvd...

they took it from there... never even put it on dvd before they pressed it :-/

zac
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Old December 3rd, 2003, 05:12 AM   #10
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Yep thats not a bad way of doing it at all. When writing to dvd-r errors can creep in, along with scratches and so on so HD or DLT is a good way. Plus you can have copy protection, Region encoding etc when using the DLT or HD method. One reason I'd say that DLT is 'better' is that some houses will charge an authoring charge when going from a HD,

Jake
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Old December 3rd, 2003, 07:44 AM   #11
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Thanks for answering my question!
Also, thanks for that link. I will go there in a few minutes.
Jake: I was talking to a sales person.


I am using the mpeg2 encoder that comes with Vegas 4.0
('Main Concept', I believe it's called, or either it's the company's
name.)

The following may be answered after I review that link you
posted, but I'll go ahead and ask: What would you suggest
as far as the VBR min/max rates as a guideline, and what
about all the other params such as 'i-frames' (I think)...
..is this similar to keyframes? And any other parameters I
should know about. I am new to mpeg2 in general. Have
only messed with AVIs. Thanks!


,Frank
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Old December 3rd, 2003, 10:00 AM   #12
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If I were you I would pick a DVD template (and leave I frame
allocation and other parameters alone) and only change quality/
bitrate levels. I personally use for VBR with CCE 0 - 5000 - 8000.
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Old December 3rd, 2003, 10:19 AM   #13
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Rob: Thanks for that recommendation! The encoder has some
defaults, one being for DVD encoding. I'll just use that and
adjust the bitrate like you suggest.


Thanks!
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