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captainmatt77
5.1 surround sound
on Oct 17, 2006 at 10:48:51 pm

Hi all,

I've got a live music shoot coming up and my client has asked that the performance be recorded in 5.1 surround. They are supplying a sound engineer who is taking care of this side of things - he is also mastering the audio (he is experienced in 5.1).

I will be editing and creating the final DVD...I've never been supplied with 5.1 surround when creating a DVD and am trying to get my head around the whole procedure. I use Adobe Encore DVD.

Is anyone able to post a rundown of authoring DVD's with 5.1 surround?

* does 5.1 mean that you are supplied 6 DIFFERENT tracks of audio or are they all combined into ONE ac3-5.1 file?
* Will file size be a problem if burning to a standard 4.7 gig DVD?

I'm really keen to get a "A-Z" understanding of what is involved.

Any help appreciated.



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Pierre-Luc
Re: 5.1 surround sound
on Oct 18, 2006 at 3:44:50 am

You'll probably get 5 or 6 separate files (.wav/.aif, mono) that you will need to encode to a single AC-3 file with a Dolby encoder, or maybe Encore can do that. You have to use AC-3 because 6 PCM channel exceed the maximum bitrate allowed by DVD-Video specs. It will considerably reduce the file size, the bitrate for a AC-3 multichannel usually is 448kbps, so with your video not exceeding 7mbps, you'll be ok.


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Frippy
Re: 5.1 surround sound
on Oct 18, 2006 at 5:31:59 am

* does 5.1 mean that you are supplied 6 DIFFERENT tracks of audio or are they all combined into ONE ac3-5.1 file?

6 wav files or 5.1 already encoded AC3.

* Will file size be a problem if burning to a standard 4.7 gig DVD?
No, all be OK. You must encode your video with maxbitrate 9800_minus_AC3's_bitrate



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riredale
Re: 5.1 surround sound
on Oct 18, 2006 at 6:16:52 am

Surround-sound is my specialty. I shoot documentaries with a 4-channel audio setup mounted atop my camera. The front 2 channels are recorded onto the HDV tape; the rear 2 channels are fed into a Minidisc recorder.

After editing the video and getting the front audio right, I pull in the individual rear audio clips and sync them, then adjust levels. Once I am happy with video and audio, I encode the 4 audio tracks into a single ac-3 file (5.1 would follow the same process, but you'd have a center channel and an "LFE" channel, which in my view is totally bogus, unless you're encoding for a 50' screen in a large theater. To each his own...).

I use Vegas for all this, which makes it a very simple and clean process. Once I have the ac-3 file and an mpv video file (the MPEG-2 encoded elementary video stream) then I can take these into the authoring program and build my DVD.

Generally, stereo ac-3 runs at about 200Kb/sec; I run my 2/2 Dolby Digital audio at 320Kb/sec. A 5.1 file would probably need a bitrate around 400Kb/sec. You look at the total running time of your DVD, then use the following formula:

overall bitrate = 600 / minutes

so if you have a 90 minute video, your overal bitrate has to be 6.67Mb/sec in order to fit on a DVD-5 disk. Subtract from that your audio bitrate (say, .4Mb/sec) and you're left with 6.27Mb/sec as your average video bitrate for your MPEG2 encoder. I would use min=0, avg=6.27, max=9.

Hope this helps.


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Frippy
Re: 5.1 surround sound
on Oct 18, 2006 at 11:23:17 am

/Generally, stereo ac-3 runs at about 200Kb/sec; I run my 2/2 Dolby Digital audio at 320Kb/sec. A 5.1 file would probably need a bitrate around 400Kb/sec/

No :)
Stetreo AC3 must be about 192..256, no more needed
2/2 - 320 - ok
5.1 file MUST be encoded at 384 or 488

Formula for calculation streams/speeds:

4.700.000 - total DVD5 size
i.e. menu ~200 megs
then - 4700000 - 200000 = 4500000 - total space for videos/audios/subs
4500000 / film_length / 60 * 8 * 0.96 = total_bitrate_for_film
If have 2 sounds - stereo (192) and 5.1 (448) then need:
total_bitrate_for_film - 192 - 448 = VIDEO BITRATE
max_bitrate_for_film is 9800 - 192 - 448
min_bitrate_for_film is VIDEO BITRATE / 2

only this formula is right!





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