Getting
Ready for DVD Authoring
With Apple's DVD Studio Pro
Page 2
Video Encoding
Steve Jobs excited everyone at MacWorld when he announced 2X (twice
real-time speed) MPEG2 encoding speeds on the new G4s equipped with
the SuperDrive. Presently, only the 733MHz machines fit this description,
which means that G4s with slower processors will encode a little slower.
By the way, this brings to mind another question many people have: Will
only the new generation processors shipping with the 733MHz and 667MHz
machines work with iDVD and DVD Studio Pro? The answer is no—any
G4 should work. In fact, DVD Studio Pro will even run on G3 machines!
It's the quick encoding that remains a question in this case since it
most likely relies on the velocity engine that is only available on
G4 processors.
In addition to the speed of the processor, there is another catch to
the 2X encoding breakthrough. It will only work if the original video
has been previously encoded in the DV format. This means that a DV stream
will encode at 2X on a 733MHz, as claimed, but any other video format
will encode as slowly as usual—more in the 10X range. Why is that?
DV video is already encoded 5:1, in a very similar fashion to MPEG2,
and Apple programmers take advantage of this to speed things up. In
fact, DVD Studio Pro uses a transcoder, not an encoder, to transform
video into the DVD-standard MPEG2 format. In order to be able to transcode
video streams, they must be in a compliant format. Quicktime is the
universal standard and works well. Those who wish to originate their
content from uncompressed video can easily do so by saving in the lossless
Quicktime Animation format. Just be prepared for long transcoding times.
Those using DV, of course, will get very nice and quick results.
Nothing prevents you from using other software-based MPEG2 encoders
to generate video streams for DVD Studio Pro. As long as the streams
are MPEG2, they can be easily imported into the software. This means
that you can use hardware-based encoders as well. They have the advantage
of working in real time, with cost for high-quality encoders being the
only drawback.
Unlike the fixed data bit rate (or high-rate VBR) used by idvd, DVD
Studio Pro lets you utilize Variable Bit Rate (VBR) encoding to obtain
a good combination of quality and storage capacity. Fixed bit rate will
encode the whole stream at a fixed rate, obviously taking up a lot of
space. VBR, on the other hand, is able to analyze the footage and apply
higher or lower compression rates depending on the nature of the footage.
Action scenes, for example, require a lot more bandwidth than a steady
camera pointing at a landscape. Therefore, VBR saves the bandwidth not
utilized by "slow" shots to be used by those shots that really
need it.
No matter what compression level you use, unless your material is short
you must calculate how much video will fit on your disc together with
the audio, stills, scripts and other necessary files. Your data rate
will normally depend on the available space, which makes the process
called bit budgeting really necessary. If you have a lot of space, you
can set your compression ratio at the low end. If you don't have a lot
of space, you must use more compression. Most commercial titles use
ratios between 2:1 and 6:1, and setting your VBR to one of these ratios
will allow the encoder/transcoder to maintain the required average bit
rate for the whole stream.
Video streams must be prepared prior to encoding/transcoding as DVD
Studio Pro and other authoring programs are not really designed for
editing. It is best to encode a single, long video segment and then
add markers inside the authoring program to create chapters. Use 720
x 480 resolution.
If your footage originated from telecined film, it is best to apply
an inverse telecine process to the footage to remove duplicate fields
prior to encoding.
Lastly, do not multiplex audio and video in a single file. Always keep
audio and video separate.
Audio
DVD Studio Pro works
with AIFF original audio streams, which can be encoded in Dolby Digital
AC-3 format to save space while maintaining high quality and enabling
multi-channel playback. Audio must be sampled at a 48KHz rate or, if
the original sampling rate is different, be converted to this rate in
order to work.
All variations of AC-3 encoding are supported by DVD Studio Pro, ranging
from two-channel stereo to 5.1 surround. When utilizing the A-Pack audio
encoding program, which comes with DVD Studio Pro, a typical rate for
two-channel Dolby is 192 Kb/s.
DVD Studio Pro utilizes a very easy to use interface that lets you assign
individual audio tracks and channels to each of the Dolby Digital channels.
This lets you premix for surround, save the files as individual AIFFs
and then assign them to the proper tracks. The program also imports
pre-encoded AC-3 files. No DTs support is available at the moment.
Miscellaneous
Owners of dual-processor
G4s have been wondering if DVD Studio Pro is multiprocessor (MP) aware.
The answer, unfortunately, is no. Only when OS-X comes out will MP machine
owners be able to take advantage of their multiple CPUs.
Some readers are concerned about copy-protection issues. DVD Studio
Pro will enable you to copy-protect your presentation so that it cannot
be duplicated by unauthorized parties. If you chose not to activate
copy protection, your content may be freely replicated.
If multiple languages is something you require, DVD Studio Pro supports
both multiple audio streams and subtitles. A friendly pull-down menu
lists all the languages available on the DVD standard, making your job
of managing multiple languages considerably easier.
Multiple camera angles are also supported.
One of the nicest menu creation features in DVD Studio Pro is the ability
to import Adobe Photoshop native files, including layers. This lets
you design your menus in Photoshop exactly how they should look on the
final DVD. All you have to do next is load the Photoshop file in DVD
Studio Pro and assign the individual layers as buttons, text, highlights,
etc. This speeds up the authoring process considerably.
While DVD authoring tools have been available for some time, the cost
has been prohibitive for most of us. These new, affordable technologies
will certainly have a big impact on our industry. Interactive DVD authoring
and distribution can be more robust and faster than interactive CD-ROM
creation. And video clients will, for the first time, be able to take
home a product that is very close to their edit masters in quality.
Will DVD completely replace CD-ROMs and VHS tapes? Only time will tell,
but the probability is very high.
