Modifying DVD Studio Pro’s default audio compression settings (increasing the data rate, for example) optimizes AC3 conversion.
Now that DVD Studio Pro is part of Apple's Final Cut Studio bundle, professional DVD authoring is available to most production pros. Having worked with DVD Studio Pro for several years, I have discovered some useful techniques that may help you with authoring DVDs.
WORKING IN SURROUND
If you plan to create a 5.1 surround audio track or if you're working in stereo but your project is large — say, two hours or so — then you'll need to process the uncompressed audio track using a Dolby Digital (AC3) conversion tool. Once your picture content has been converted to MPEG-2, your two-hour movie/concert file may be close to 4 Gigabytes, depending on the compression settings used. Uncompressed stereo audio for this project might be about 1.2 GB. Requiring more than 5 GB, your project won't fit on a standard DVD-R, and compressing the audio track to AC3 yields an audio file of about 200 Kb, enabling a project build onto a 4.7GB DVD-R.
The Final Cut Studio bundle includes the Compressor video and audio compression application, and its default settings are set for use with professional film encoders. However, users can tweak these parameters to their taste. To make my AC3 file sound like the original uncompressed PCM track, I changed several values. Within Compressor's Inspector window, where these settings live, I selected the Audio tab and increased the data rate to 256 kbps (rather than the 192kbps default) for improved response with stereo tracks. Under the Preprocessing tab, I set the compression preset to none and de-selected the lowpass filter and DC filter boxes.
These same changes to the settings also work for surround applications, but in that instance, I increased the data rate to 448 kbps. These tweaks typically result in an AC3 file that sounds like the original, but doing some experimentation to find the settings that work best with your program material will really pay off.
TIMING IS EVERYTHING
If you're creating a video and audio track in DVD Studio Pro by assembling several short clips together sequentially on the same timeline, then be aware of potential differences in the length of the audio file as compared to the video file after the audio is converted to AC3.
As an example, I have a movie file called “events .mov” with a duration of 00:03:27:09. After converting the video to MPEG-2, the video and uncompressed AIFF audio file are still the same length. But after converting the AIFF file to “events.ac3,” the duration may change to 00:03:27:08. The AC3 file is now one frame shorter. By itself, this is not a big deal. However, if your track contains several clips like this, then you'll introduce an offset between the audio and video that increases with each clip added to the timeline, putting your audio out of sync with the video.
To solve this problem, leave DVD Studio Pro's Inspector window open and compare the AC3 file to the M2V file each time you bring a new A/V pair onto the timeline. Inspector lets you make adjustments to the start and duration of audio files. DVD Studio Pro does not allow gaps between video segments, but it does allow them between audio segments. So if your audio file is a frame shorter than the video, then you can compensate for the difference when you bring the next A/V pair onto the timeline and adjust the start time (not clip start trim) of the audio clip by +1 frame.
The key here is that each A/V pair must have the same start time and you must verify this as you bring them in one pair at a time. If you bring in all of the audio and video clips and then try to make adjustments, you may not be able to do so if the next segment on the timeline blocks the necessary adjustment.
Most people use DVD Studio Pro as an authoring tool, but the program is highly useful in the studio during production for writing multichannel stems as pass-around references for music, dialog and effects elements and/or premixes. In DVD form, these stems can be easily screened or auditioned (and inexpensively duplicated) without the need for elaborate audio playback setups.
And DVD Studio Pro is equally useful at the other end of the production: presenting multiple reference mixes to clients, producers, directors, etc. Reducing the normal 5 to 8Mb/sec video bit rate to a low-res “workprint” setting of 3 or 4 Mb/sec will allow plenty of bandwidth to accommodate the bitstreams of three or four simultaneous audio soundtracks — all in picture sync and easily switched for instantaneous A/B/C comparisons via the audio select button on any DVD player remote.
Running the current software is a must. New audio features in DVD Studio Pro 4 include support for DTS file imports, 96kHz audio import and support for the new HDVD format. More information about upgrades, crossgrades and the latest version of DVD Studio Pro, Compressor and the Final Cut Studio package can be found at www.apple.com.
Now the co-owner of Video 4, a video/DVD production studio in Corralitos, Calif., Kevin Monahan spent 20 years doing sound design and product development for E-mu Systems.