by John Hess
The purpose of this article is to become familiar with the basics of DVD authoring so that you can take that masterpiece of a film you’ve edited on a favorite NLE and put it onto disc so others can enjoy it.
For this article I will mainly be referencing Adobe Encore CS3. Although some of the terminology might be Encore specific the general idea of DVD authoring should be applicable to any DVD software.
If you’ve watched any Hollywood DVD, you know that DVDs are broken down into two basic parts – Menus and Movie Assets (called Timelines in Encore). This goes for both standard def and the new blu-ray format.
Menus are screens where the viewer can make a selections. It’s helpful to think of menus as webpages – with links to other webpages or content. The viewer can stay on a menu for as long as the user wants to (unless the menu is programmed to automatically advance).
The Movie Assets are video and audio files – like the film or behind the scenes clips of a DVD. Asset files, when activated, play through their content without stopping unless interrupted by the user.
The following flowchart, made from Adobe Encore CS3′s flowchart viewer, shows a very basic DVD layout:
This flowchart is meant to be read from left to right. When the DVD is inserted into a DVD player, it loads up the “First Play” item which in this case is a menu titled “Home Menu”. From the home menu, the user can select one of four buttons – each with a corresponding assets attached (cleverly titled Movie 1, Movie 2, Movie 3, and Movie 4). When the assets are done playing, the take you back to the home menu.
The following flowchart is one that you’ll find on most DVDs you rent from your favorite rental store.
In this particular set up – the first play is set to a menu with thee options – one of which is to play Movie 1, the other two options take you to Menus (a Chapters Menu and a Special Features Menu).
The chapter menu contains links to chapter markers in the Movie Asset and another link back to the home menu.
The special features menu has four buttons of it’s own – one to play a “Making Of” movie, one to play the “Trailer”, one button to play the movie but with a secondary Audio track turned on (“Director’s Commentary”) and the last one to take the user back to the original home menu.
When you create your DVD you should consider what kind of features you want to include and design your layout appropriately.
Menus, as previously stated, are screens that allow the user to make a selection. These screens may be static or include video/audio. Adobe Encore integrates Photoshop files natively – allowing you to edit your menus using Photoshop. Check the Help files with your DVD authoring software for how to create/edit menus.
This is the section of DVD authoring that most people get hung up on. All DVDs use MPEG compression for their video files. When you finish editing in your NLE and you’re ready to export to DVD, you’ll want to create an MPEG compressed file. Most of the time what you’ll be creating is a Video only M2V file and an MPEG audio file (MPA) that’s synched up to the video file. Being separate allows you to add multiple audio tracks to your DVD (up to 8 different tracks for different languages and for director’s commentary).
MPEG compression is a much maligned compression format. How MPEG works (roughly) is the computer divides up your video into key frames called I frames usually one every 15 frames or so. Then the computer compares each frame to that I frame and writes the differnces into P frames and B frames – it’s all alphabet soup and I’m not going to pretend I understand it. And you don’t have understand it to make great DVD video. Although you’ll hear people say how terrible MPEG is – it’s actually an amazing leap in technology that allows us to put hours of video content on a single disc.
When you export from your NLE, make sure you select MPEG2 (DVD). Most modern NLEs have several presets for exporting a DVD ready M2V files. Here is the advanced panel from Adobe Premiere CS3′s Adobe Media Encoder:
A couple things to point out here that will be universal to all encoding software…
First of all, all DVDs are encoded using the DV settings of 720×480. If your project is standard 4×3, then you will be selecting a 0.9 pixel aspect ration. If your project is 16×9, you will be working with a 1.2 pixel aspect ratio. Either way, you will be encoding a file that’s 720×480.
For frame rate you have three options: 23.976, 29.97 drop frame, 29.97 (non drop frame). 23.976 is just a fancy way of saying 24p (with the drop frame) so if you’ve editing your project at 24 frames a second, this is the setting for you. If you’ve shot it stardard 60i choose either 29.97 drop frame or non-drop frame. As someone who still does stuff for broadcast – I stick to the standard drop frame.
As a note – for those of you who shoot 24p. Encode your DVD in 24p and let the final DVD player introduce the 2:3 pulldown. Let the DVD player introduce the 3:2 pulldown when it plays for television. Plus a lot of DVDs and TVs are now capable of displaying progressive 24p footage so you don’t want to mess around adding funky jitters to your footage unless you have to (like if you’re going to broadcast)
The last bit in the Basic Video Settings box of Premiere is the Field order and this deals with interlacing. Mini DV’s field order is Lower First so if you shot it that way and want to maintain consistency – use lower field first.
HDV is an upper field first format but if you downconverting to Standard def those fields will probably cause some funky interlacing artifacts in the downconversion process. I usually deinterlace the HD footage before downconverting. Then it’s up to you whether you want a more filmlike progressive image or a smoother action (pick either lower or upper fields).
Encoding: Bit Budgeting
The next box is where the fun begins. Since MPEG is a compression format we have a few options on how we would like to compress our footage. We want to maximize our quality without being too big as to fit on a DVD.
Remember how MPEG works by looking at keyframes called I-frames and then fills in the missing frames between? Well the more we compress a video file, the less information the computer has to fill in the missing frames. So for best quality – we want to have the highest bitrate possible which for DVDs is 9 Megabits (bits are 1/8th of a byte). That’s all fine for a project that’s less than an hour long, but a single layer DVD is limited to only 4.7 gigabytes. In order to fit longer projects on a DVD we’ll need to compress our footage.
Compression comes in two flavors:
CBR: Constant Bit Rate
The amount of compression remains the same throughout your video
VBR: Variable Bit Rate
The amount of compression increases or decreases depending on the action in the video. You have two options here – 1 or 2 passes.
Which format should you use? For projects that are less than 1 hour in length you can go with CBR with a setting of 9 Megabits per second. This setting is the quickest to render and offers the highest quality.
Now if your project is longer than 1 hour, some mathematics may be involved – you can use a bit budget calculator or do your own math. I run through an example here with a project that is 122 minutes long.
First we start with the size of a DVD:
4.7 gigabytes = 4700 megabytes
Then calculate number of megabits
4700 megabytes x 8 bits/byte = 37600 megabits
I shave off 10% just to be on the safe side. So a standard DVD-R has about 34000 megabits for us to work with
Next look at the total length of your project – let’s say our feature film is 122 minutes long.
122 minutes x 60 seconds/minute = 7320 seconds
Now lets calculate our maximum megabits/sec for video and audio:
34000 megabits max / 7320 seconds = 4.644 megabits/sec
So we have 4.644 megabits/sec to share between the video and audio track. In Premiere you can change the compression for the audio – a standard for good audio is 192 kilobits per second – that’s .192 megabits
So now let’s subtract our audio data rate to get our maximum bit rate for the video:
4.644 megabits/sec (for video and audio) – .192 megabits/sec (audio) = 4.452 megabits/sec for our video.
So if we encode our video at 4.452 megabits CBR we’ll be able to fit all 122 minutes onto a DVD.
Now here’s where Variable Bit rate can come in handy. Variable bit rate will look at your project footage and adjust the bit rate depending on how much action is occuring in the frame. A static shot of a person giving a lecture will look good with a lot less bandwidth (bits/sec) than an action packed shaki-cam shot of a police chase. Why waste space on a DVD especially when it’s short supply.
With Variable Bit rate, we can set the average bit rate to 4.452 megabits/sec, the maximum bit rate to 9 megabits/sec and the minimum to 1.5 megabits/sec. This will tell the encoder that the bit rate average over the file needs to be 4.452 megabits/sec or lower and when the frame gets busy – increase the bit rate as high as 9.0 and when nothing’s going on, get it down to 1.5 megabits.
With Variable Bit rate, you have the option of running 1 or 2 passes in Premiere (other software packages may have more options). The more passes you run, the more efficient the compression will be and the higher quality the end result. The drawback is 2 passes take twice as long as one.
But if you have the time – 2 passes will almost always generate better looking video and a smaller file size than 1 pass.
If you’ve made it this far you understand the fundamentals of DVD authoring and encoding. Each DVD authoring program will have it’s own specific process on how to set up menus and assets but the basic concept of DVD navigation and encoding apply to all programs. In the next article, I’ll explore some creative applications of DVD that go beyond the familiar DVD.
John Hess is a Professional Filmmaker, Filmmaker IQ Contributer and Team Member.