Rivergate Software Inc. - makers of DVDAfterEdit

Requires DVDAfterEdit Standard

Part 1: Introduction and Preparing the Project

This article was written before DTS support was added to DVD Studio Pro. However the "Replace VTS" function is one of 'Edit's most powerful features, also allowing us to modify subtitle streams in exisiting features or remove or change sections of video, for example. The procedure outlined here applies to all these scenarios. It can also be used with the output of ANY authoring application, not just DVDSP. To jump directly to the section on using the Replace VTS function straight away, please click here, however many people may still find much of the discussion in sections 1 and 2 helpful.

Introduction

DTS audio is one of the DVD format's super-high-end features that simply hasn't been available to DVD authors like us at a realistic price - until DVDAfterEdit came along. This article describes how to use the "Replace VTS" function to incorporate DTS audio into your existing project, in a suprisingly straightforward way.

Using the technique to achieve DTS support is quite an advanced use of the Replace VTS function, but it can also be put to other, more straightforward purposes - you could use it to replace a copyright logo on a disc one of your customers has licensed, for example. Something that previously would have required days of ripping and re-authoring can now be accomplished in a matter of minutes !

I sometimes choose to use this method for adding DTS to DVDs even though we now have a Creator system, because it's just so much faster to put many types of new projects together in DVD Studio Pro.

Something which should be made clear from the outset is that to use DTS audio, you will need a DTS encoder, like the one made by Minnetonka Audio (http://www.surcode.com/low/dvdDts/dvdDts.htm) as well as DVDAfterEdit and your normal authoring software . You will also need a way of multiplexing (building) the DTS audio stream, along with your video, into a DVD file structure (VOB file). Before I persuaded SRT to invest in the Sonic system, we had this encoding and multiplexing done for us by another authoring company who already offered DTS. I'll cover this in detail in the article, but for now it's important to realise that (unusually !) at the moment DVDAfterEdit can't offer a complete solution. In the future, though, who knows...

The technique described here has been tested on DVD projects authored using DVD Studio Pro versions 1.5.2 and 2.0, and can be adapted to work with any other system too.

Overview of the method

These are the steps we are going to work through:

1. Author your project as normal, so you can set-up and test Audio Select menus and/or audio-related scripting. Restrict the data-rate and total size of your video stream to allow "space" for the extra DTS track, by using an extra PCM audio stream as a "place-holder" in your project
2. Build and test the project
3. Encode your DTS Audio stream
4. Use a suitable authoring package to multiplex your DTS audio with your other video, audio and subpicture assets into a VOB file.
5. Use DVDAfterEdit's "Replace VTS" function to replace the original VOB file in it's entirety with the new one containing the DTS audio, but nevertheless retaining all the navigation commands from your original project.

Before we get into the details though, a little background may be useful.

What is DTS Audio?

DTS is an audio compression codec developed by the company Digital Theatre Systems, and does the same job as Dolby Digital (AC-3) - offering high-quality surround-sound in cinemas and on DVDs. It is becoming more and more popular on DVD releases, especially music titles. It has various Pros and Cons:

There are debates raging in Pro Audio circles about whether DTS really does sound better or not, and whether the Pros outweigh the cons, but meanwhile more and more of our customers are asking for it, and the customer is always right!

So, lets look at each of the stages more closely.

The Method In Detail

1. Author your project with a dummy "placeholder" audio stream.

We are lucky that the DVD spec commands which control navigation and interactivity only refer to "Audio Streams", without specifying what format they are in. A familiar example showing why this is useful is that we can safely author a project (which will eventually have surround-sound) using two stereo audio streams - one as a dummy placeholder - while we wait for the surround mix to be completed. We then replace the second stereo stream with the 5.1 stream at the very last moment. All our "set stream" commands will still work, even though we've changed the contents of the stream.

Similarly, because the method described here preserves all the existing pre- and post- commands from your chosen authoring package (scripting, in Abstraction Layer terms), we can safely add an extra audio stream of any format to our project while authoring, pretending to ourselves that it is a DTS stream, and build all the control we would like for it into our project. Then at the end of the process when we exchange our original VTS for one which really does contain DTS, everything will carry on working just as we intend.

The illustration below shows an example "track" (title) in DVD Studio Pro, where the third stream is the dummy placeholder audio track.

Notice that the track has a pre-script which sets the audio stream to the value of the variable ChosenAudioStream. Elsewhere in the project there is a menu where this value is set depending on the choices made by the user. Using our method here, all this interactivity will be preserved after this track has been replaced by one containing DTS audio !

We do have to be careful about one point though - maximum data rate and bit-budgeting. The DVD spec specifies that any playback stream (video, audio & sub-pictures) should not exceed a maximum rate of 10.08 Mbps. So in a typical single-language feature film with stereo and surround sound-tracks, this means our video data-rate can peak at a maximum of 9.4 Mbps:

Whereas with an extra DTS stream at it's highest-quality, this is significantly reduced:

So we need to adjust the parameters of the video stream when we encode, and ensure that our encoder actually complies with them ! This is especially important if you will be getting the DTS encoded and multplexed by another facility, since the last thing you want is to send all your assets away and be told the data rate is too high.

We also need to take care that there is enough space for all the assets on our disc. High-quality DTS files take up over 3 times as much space as 5.1 AC-3, because they have a data rate 3 times higher.

A great tip to avoid mistakes is to use a stereo PCM (AIFF or WAV) file as the "dummy" or placeholder track when authoring. This has the same data rate and size as a high-quality DTS stream, so if your project has enough space for this file, it will have enough space for the final DTS stream.

2. Build And Test The Project

Write your project to hard drive, as though you were going to write a DVD-R or DLT. This will create a VIDEO_TS folder, a duplicate of the file system which will eventually end up on the finished disc, and which we will later open with DVDAfterEdit to swap the DTS audio into. As usual, test everything about this project fully, especially audio behaviour and scripting - bearing in mind of course that we have a "dummy" PCM stream instead of the eventual DTS stream.

Now move on to Part 2