Rivergate Software Inc. - makers of DVDAfterEdit

Requires DVDAfterEdit Standard

Part 2: Encoding DTS & Multiplexing the New VTS

3. Encode the DTS audio tracks

As I mentioned in the introduction, you will either need to own a utility like Surcode DTS-DVD, or ask someone else to do the encoding for you. If you decide to go the later route, it's probably best to find someone who uses a software encoder, mainly to keep sync issues straightforward. Remember you won't be able to trim or add frames to a DTS audio stream in your authoring application as you might with AC-3 or PCM. If the facility you choose do use a hardware encoder, you will have to supply the mix on multitrack digital tape, with timecode and in/out points.

If you go the software route, just as with A-Pack you need to verify the sync of the audio - the easiest way is probably to load the main left and right tracks up in a video editor like Premiere or Final Cut and verify that when the start points are lined up, it sounds & looks right.

I'll give a brief example of encoding using SurCode DTS_DVD - if you choose to do it yourself it is very straightforward - similar to encoding with A-Pack or a similar utlilty, but with fewer parameters to set. If you are using an external facility, you will still find it useful to understand the following, to help explain to the people who are doing the work for you exactly what it is that you want.

Incidentally, wherever possible I would suggest finding a facility who can both encode and multiplex the DTS audio for you - somewhere like this is more likely to have a full understanding of everything that's involved with the process, so you'll have less supervising to do, and there's less possibiity for mistakes.

You should have five or six 48 kHz WAV or AIFF files for the 6 channels of your surround-sound mix. DTS supports fewer tracks as well, but is most commonly used for surround-sound. If the encoder supports it, you will get slightly better quality encodes if the files you use are 24-bit rather than 16-bit. Wherever possible I would suggest you have the files encoded at 1.536 Mbps, rather than the lower 768 kbps data rate, since in my opinion it's barely worth the extra effort and expense of DTS unless you use it's highest quality setting. On the other hand, if the bit-budget is tight, and your customers insist...!

Once you have loaded your source files into the right "slots" as shown above, you need to name the Destination file, and choose a location for it.

At this point you will also need to choose the format of the DTS file you are going to create. There are three choices in Surcode - DTS Padded (*.dts), DTS Compact (*.cpt), and DTS WAV (*.wav). You'll need to choose the right one for the authoring application which is going to be used to multiplex (combine)the video & audio streams. For Sonic DVD Creator, the right one is the DTS Compact (*.cpt)format.

Finally we simply need to select the encoding options, and hit "Encode". The only option we haven't already discussed is the "Attenuate Rear Channels 3dB" setting. As with Dolby Digital, this is here because for playback in cinemas, the rear channels are normally attenuated (reduced in level)by 3 dB. (Surround audio is often quieter, so can be encoded louder and turned down on playback, giving theoretically better quality.)So when mixing for film, cinema people mix the rear channels 3 dB louder to compensate. However a Home Cinema setup doesn't reduce the level of the rears, so if your material has come from a cinema, you should tick this box or the rear channels will sound 3 dB too loud. If you aren't sure whether to use this option or not, check with the people who supplied the audio to you. If they don't know, a quick test encode with an AC-3 file and a correctly setup 5.1 system should shine some light.

That's it - one way or another, you (or the facility you are using)should now have an encoded DTS file ready to be multiplexed along with any other audio and possibly sub-picture streams (Subtitles, button highlights)that you need.

I'll cover the requirements for this in a moment, but for now let's pause for a moment to look in a little more detail at what a VTS actually is.

Background - What is a VTS ?

When working with many of the popular authoring packages, the major video assets in a DVD project are commonly referred to as "Titles", "Tracks", or "Movies". The video for these is stored in large Video Object (VOB)files on the disc.

Information about each VOB file is contained in a corresponding information (IFO)file, and the DVD player reads this file and uses it as a set of instructions telling it how to play back the video contained in the VOB file.

A VOB file can contain the video for only one title or several. So for example, one VOB might contain all the video for the disc - say with the main feature first followed by a bonus feature - in which case the IFO file will describe two different playback sequences or titles. The first title instructs the player to play the section of the VOB relating to the main feature, the second describes the playing sequence for the bonus feature. The titles are each defined by a Program Chain (PGC), which is simply a description of what sequences of video the player should play, and in which order.

The title PGCs are grouped together in Video Title Sets - the point being that all the titles in a particular set use video from the same VOB. (This means they must all have the same aspect ratio and audio/subpicture streams, by the way)Simpler DVDs only allow the video in the VOB to be played back in one particular order, and so only have one title per VTS - ie. a "set" of one !

As you can see in the illustration above, the VOB files are therefore labelled with names like

* VTS_01_1.VOB - the VOB containing the video used by VTS 01 - and
VTS_01_1.IFO - the instruction file describing the Title PGCs for that VTS

So to summarise - a Video Title Set (VTS)is a complete description of the ways in which a particular DVD can play back the video contained in it's corresponding VOB file. It can contain one title PGC, or several. If we want to replace the video in a VOB file with a new version containing DTS audio, for example, then by necessity we need to replace the entire VTS.

As it turns out, if we aren't using authoring features like "stories" or "playlists", many authoring packages only create one title per VTS, which makes replacing the VTS using TFDVDEdit very straightforward, as we shall see. If your project has a more complicated VTS structure though, with multiple PGCs, you can use TFDVDEdit to recreate that VTS PGC structure using it's amazing Title List Editor - but that's a whole different article...!

4. Preparing the DTS VTS - Multiplexing to create a new VOB & IFO file

Let's remind ourselves where we're up to - at this stage we have an an encoded DTS file, and our project's VIDEO_TS folder on a hard drive. One of the VOB files in the folder holds the multiplexed video stream containing the video we want to add a DTS soundtrack to, currently with a "placeholder" PCM audio stream. We now want to create a new VTS, containing the DTS audio stream, to replace the existing one with. This means generating a new VOB file and IFO file, for which we need an authoring package which supports DTS. Currently this means Sonic Scenarist, DVD Creator / DVD Fusion (with the Advanced Authoring Pack), or Spruce Maestro.

I will outline the process to create a suitable VIDEO_TS using DVD Creator here, hopefully giving you enough of an insight to effectively communicate what you need to the facility who do this for you to deliver.

All that's needed is to create a project containing a single Title Set structured in exactly the same way as your original Track or Movie - ie. with the same layout of audio and subpicture streams except that it will include a DTS stream.

You will need to supply the following, either on DVD-R or a firewire hard-drive :

• The MPEG-2 (m2v, mpeg)video file
• Any non-DTS audio
• Either the encoded DTS file or the raw 5.1 streams if you need them to encode it too
• Any subpicture elements for the VTS - subtitles, button highlights etc.
• An I-frame-accurate list of chapter points

The assets will need to be imported into the DTS authoring application. Creator and Scenarist call everything by their "proper" names (VTS, PGC etc), which makes things a little simpler when talking to authors about your requirements. By default every new project contains an empty VTS, so all that's necessary is to double-click on it to open it up and drag the MPEG-2 video into it. Then the audio must also be dragged across, and assigned in the same way as it was in your original project. So, in my example Stream 1 is stereo AC-3, Stream 2 is 5.1 AC-3. Stream 3 was the dummy PCM stream in my original project so here it contains the DTS stream. This ensures that all the interactive control of our original project will work exactly as expected.

Make sure the attributes of the audio and video streams are set correctly - the video aspect ratio, and the language settings of the audio streams, for example. These can be adjusted later in TFDVDEdit, but it's better to get them right from the start. Any subtitles and button highlights must be correctly setup at this stage.

It's also best for all the chapters to be added in the DTS application as well. Again, this can be done "after the fact" in TFDVDEdit, but my personal preference is for the imported DTS VTS to be "plug in and go". The illustration above shows a project with one VTS, containing the video and audio streams, including the DTS stream. Also shown are the settings for one of the chapters - if you've been using 'Edit for a while you'll recognise many of the properties - the chapter is a Part Of Title (PTT)Program, with seamless playback enabled.

Finally the project needs to be built to the hard drive, so you'll end up with a second VIDEO_TS folder, containing just one VTS VOB file and IFO file. This is then ready to be "Replaced Into" the original project, over the top of the VTS with the dummy PCM stream. If someone else is doing this for you, ask them to send the new VIDEO_TS folder with the DTS VOB back to you on DVD-R or a firewire hard drive.

Finally, bear in mind that the above creates the very common and straightforward VTS structure of only one Title PGC per VTS. If you or your authoring application have created more complex VTS PGC structures in your project, you will have to recreate these using TFDVDEdit's Title List Editor, which will be covered in another article.

Now move on to Part 3