RE: Splitting Video & Audio Streams

Maverick wrote on 7/5/2003, 6:52 PM
Hi

I'm learning fast and enjoying using DVD Architect but there is so much not really explained in the manual.

I know I can render to MainConcept mpeg2 and, apparently, that will pay in a DVD player well enough if I use the default DVD PAL setting.

But what would be the advantage of splitting the Audio and video into streams, rendering them separately and puttingtyem back together again in DVD Architect. I have read many posts where audio sync is out.

Do I really need to do this for just a stereo soundtrack? Would I get better Audio and/or video in the final rendition?

Thanks again for all help offered.

great fun, isn't it?

Comments

BillyBoy wrote on 7/5/2003, 9:19 PM
The point is you don't have to change anything if you don't want to. I've burned a bunch of DVD's in DVD-A using the generic Vegas DV MPEG-2 templates. DVD simply will recompress the audio portion. If you wish you can use the supplied DVD-A template for JUST THE VIDEO, then also render the audio as AC3 seperately IF you are in the NTSC world, which you aren't and if I understand correctly PAL accepts the MPEG-2 steam as is, so if that's true then it won't recompress anything.

It there an advantage to one way or another? Not really even for those of us in the NTSC world. The only real difference is either you while still in Vegas render the audio seperately as AC3 or you just let DVD-A recompress the audio which it will do automatically. Of some minor benefit would be you'd know up front how much room your project files would take rather then just letting DVD-A recompress. Would the audio quality be better using one method over the other? No.
mikkie wrote on 7/6/2003, 9:07 AM
FWIW, 'bout the only reason I'm aware of for splitting the streams, is so some other app will accept the file as input - there are some flags for example that you might set for/in the mpg2, and restream only accepts video streams... some DVD authoring apps only take separate streams... that sort of thing.
Maverick wrote on 7/8/2003, 7:46 AM
I amy be talking rubbish here but, so far, when I have Prepared the DVD the Audio section from the MPEG-2 file is re-rendered. On the same DVD I have added a music compilation but pre-rendered these in V4 as AC3 and these do not get pre-rendered. So, is it a fact that DVDs require audio as AC3?

Cheers
roger_74 wrote on 7/8/2003, 7:56 AM
"Would the audio quality be better using one method over the other? No."

The DVD-templates in Vegas are all MPEG 1 Layer 2 audio, as far as I can see. That means you're recompressing from MPEG 1 Layer 2 to AC3, which is a very, very bad thing to do.
swampler wrote on 7/8/2003, 8:19 AM
In DVD-A, click on the "optimize DVD" button. You probably have audio set to automatic which will typically re-encode audio to AC3 2.0 (in my limited experience). You need to change this setting to match the audio you currently have so that it won't rerender.
Maverick wrote on 7/8/2003, 8:30 AM
'In DVD-A, click on the "optimize DVD" button. You probably have audio set to automatic which will typically re-encode audio to AC3 2.0 (in my limited experience). You need to change this setting to match the audio you currently have so that it won't rerender. '

I only have four options;
Automatic
AC-3 5.1 Surround
AC-3 Stereo
PCM Stereo

There seems to be no mention of MPEG. What about PCM - is this the same?

Cheers
roger_74 wrote on 7/8/2003, 8:34 AM
PCM is uncompressed audio.
Maverick wrote on 7/8/2003, 8:41 AM
In 'PCM is uncompressed audio.'

In which case am I missing an option somewhere so that DVDA doesn't recompress the MPEG-2 file or do I use PCM - assuming this to mean it will not compress the audio stream no matter what it is already compressed as.
roger_74 wrote on 7/8/2003, 8:56 AM
I don't think you're missing anything. It seems DVD Architect doesn't want to burn MPEG audio. I would recommend that you render a separate AC3-file.
Maverick wrote on 7/8/2003, 9:03 AM
Thanks.

I haven't actually watched the DVD as yet (it's of my parents' 50th wedding anniversary) but they are please with it. I'll have time to view it later.

I have heard from here problems with audio sync when rendering separate audio files. Is there something I can do in adnvance to minimise this possibilty?

Cheers
mikkie wrote on 7/8/2003, 10:24 AM
"So, is it a fact that DVDs require audio as AC3?"

Irrespective of DVDA, DVDs can have mpg audio, ac3, or dts if I'm not mistaken - http://www.thedigitalbits.com/officialfaq.html might have more info.

"I have heard from here problems with audio sync when rendering separate audio files. Is there something I can do in adnvance to minimise this possibilty?"

Actually no, as these are already separate streams in an mpg2 file, not interleaved as with an avi. You should in theory be able to demux, mux at will, but the prog.s used can often alter the files, resulting in among other things sync problems. Not as big a prob as it used to be, though superstitions persist.

There are audio and video stream delay flags, which you can set to fine tune sync if you have a problem where audio is off by a constant amount. Generally shouldn't have to bother though with vegas.

"The DVD-templates in Vegas are all MPEG 1 Layer 2 audio, as far as I can see. That means you're recompressing from MPEG 1 Layer 2 to AC3, which is a very, very bad thing to do. "

Should be a generic DVD NTSC stream that includes mpg audio, and the rendered output should work as is depending on how you author the DVD. Otherwise, regardless the template can check the box to render separate streams for compatibility with other authoring apps as needed. The templates for DVDA I think render video only, and you're supposed to do the ac3 in Vegas as a separate step before import - think there was/is a script to do this as one step.
swampler wrote on 7/8/2003, 1:12 PM
Mpeg audio is NOT a standard for NTSC DVD discs, but it is in PAL. Maybe this is why DVD-A doesn't let you pick MPEG audio?
roger_74 wrote on 7/8/2003, 1:33 PM
I don't think MPEG audio is a problem for NTSC. The players don't really care about TV systems. Everything is stored in the same way anyway. Multichannel MPEG is another story, because I don't think there are any decoders available outside Europe. And even in Europe they are scarce, luckily they changed their mind and went with Dolby Digital.
swampler wrote on 7/8/2003, 1:41 PM
Most NTSC players will play MPEG, but it is not guaranteed.
roger_74 wrote on 7/8/2003, 4:15 PM
That's true.

All things considered, I'd just go with AC3. MPEG 1 sounds very bad to me. It can be ok on builtin TV speakers, but when hooked up to better speakers the difference is clear.
Maverick wrote on 7/8/2003, 9:08 PM
Thank for all the tips.

My next project I am already rendering as seperate audio & video. So far it's showing as taking an hour with another 6 to go for a 40 minute project. There's quite a few overlays and track motion, though so I suppose on a 1800+XP system that must be about right.

Cheers
Maverick wrote on 7/8/2003, 9:08 PM
Thank for all the tips.

My next project I am already rendering as seperate audio & video. So far it's showing as taking an hour with another 6 to go for a 40 minute project. There's quite a few overlays and track motion, though so I suppose on a 1800+XP system that must be about right.

Cheers