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5.1 audio query

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Jason Cork
5.1 audio query
on May 14, 2009 at 3:54:36 pm

I have a source video on HD-Cam which has a 5.1 surround audio track. I know nothing about the encoding from tape side of things... someone else will be doing this. But when it comes to the authoring in Encore (CS4) I'm wondering if having a 5.1 track poses any issues? Would I simply be supplied with a single audio track, as I would with 2.0 audio? Or is it more complex than that? Thanks in advance...


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Jon Geddes
Re: 5.1 audio query
on May 14, 2009 at 8:41:38 pm

Encore does not support encoding of a 5.1 track, however it will burn a 5.1 ac3 track if it's already been encoded from a different program.

So, knowing this, if you do anything that causes encore to have to re-encode your audio, such as combining multiple clips into a single timeline or trimming the audio clip, then it will not output 5.1 audio.

5.1 Audio is contained in a single .ac3 file.

Jon Geddes
Motion Graphics Designer
http://www.precomposed.com


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Joe Bowden
Re: 5.1 audio query
on May 14, 2009 at 9:05:24 pm

Encore will only import a 5.1 audio stream that is compressed as either AC3 or DTS.

I suspect your camera creates a muxed MPEG-2 that has the video and audio combined, which probably will import but will be problematic. Find an application that will strip the audio out, and if it's Dolby Surround or DTS, then you're in luck, and you should be able import the video and audio streams into Encore without the need to re-encode.

Otherwise you'll have to encode the audio to those formats elsewhere, and then import them for use in Encore; or mix them down to stereo audio and import that into Encore.

Edit: you may be able to find a freeware application that can strip MPEG-2 program/transport streams at videohelp.com



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Jason Cork
Re: 5.1 audio query
on May 14, 2009 at 9:35:28 pm

OK, well, as mentioned, the source video, which has been edited and mixed etc. is on HDCam-SR at present and I will be giving this tape to another company to encode for me, then supply me the separate audio/video tracks on disc.

So from what you're saying, I need to specifically instruct them to encode the audio track as an AC3 track and supply this to me? Does anything special need to be done their end? And then I just import it into the project with my video?

I have previously worked with separate video/audio tracks in Encore anyway, so no problem there. But I'm a bit confused by something Jon says...

"...if you do anything that causes encore to have to re-encode your audio, such as combining multiple clips into a single timeline... then it will not output 5.1 audio."

Won't any audio be combined in the timeline anyway, when I tie it in the with the video track?


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Jon Geddes
Re: 5.1 audio query
on May 14, 2009 at 9:50:09 pm

[Jason Cork] "Won't any audio be combined in the timeline anyway, when I tie it in the with the video track?"

No. If you are using a single m2v file and ac3 file, you have nothing to worry about. However, if they provide you with multiple video and audio clips for some reason (like one clip for each tape/disc captured), then you need to place the clips in separate timelines in Encore.

By combining, I mean the following:
Let's say you have 2 Clips, Clip(A) and Clip(B). Each clip is comprised of an audio and video file. You can place Clip(A) and Clip(B) into a single timeline in Encore.

Encore supports placing multiple videos into a single timeline, however it then has to re-encode the audio. If it does this, then it will downconvert your 5.1 stream into 2.0.

Jon Geddes
Motion Graphics Designer
http://www.precomposed.com


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Jason Cork
Re: 5.1 audio query
on May 14, 2009 at 10:49:01 pm

Ah, ok. I understand. Thanks for explaining.

How would I go about adding the 2.0 track, so that it could be selected from the DVD menu as an alternate, for someone who doesn't have a 5.1 sound system?


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Jon Geddes
Re: 5.1 audio query
on May 15, 2009 at 2:22:06 am

A stereo 2.0 track is not really necessary as the dvd player can downmix a 5.1 stream to 2.0 on the fly. However, if you want full control over the downmix, you can create your own and place it in the timeline below the 5.1 mix as an alternate audio.

Jon Geddes
Motion Graphics Designer
http://www.precomposed.com


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Jason Cork
Re: 5.1 audio query
on May 15, 2009 at 10:00:28 am

Is that true of all modern DVD players then? Standalone and computer based? I remember some discs I had years ago used to have separate 5.1/2.0 tracks. But is that generally not the case nowadays? Is it just due to advances in technology of the players?


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Jon Geddes
Re: 5.1 audio query
on May 15, 2009 at 4:32:30 pm

I'm pretty sure all DVD players can downmix 5.1 audio. I have not heard of any that cannot.

Many old dvd's have a 2.0 stereo and 5.1 track. I'm assuming this is so they could have complete control over the downmix, instead of allowing the player to do it.

If you recall, old dvd's weren't always designed optimally. Remember when widescreen movies weren't anamorphic? They would just letterbox a 4x3 stream and it looked like garbage.

Using a single 5.1 track on the disc provides more space for the video allowing for higher quality and less compression.

Jon Geddes
Motion Graphics Designer
http://www.precomposed.com


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