Standards and Practices for Authoring Dolby
®
Digital and Dolby E Bitstreams
21
1. Record the Dolby E stream so audio and picture are in sync on tape. This requires
advancing the source tracks one frame before encoding to compensate for the one
frame of delay in the Dolby E encoding process. This method maintains audio/picture
sync on the recording media to facilitate editing. Upon decode of the Dolby E data,
the video will have to be delayed one frame to compensate for the one frame of delay
in the decoding process.
2. Record the Dolby E data so the decoded Dolby E data stream will be in sync with
video upon decoding of the data stream.
When using Dolby E with standard definition video, this requires advancing the audio
two frames prior to encoding. This compensates for the single-frame delay during the
encode cycle and the additional single-frame delay on decode. This method is useful to
ensure that there will be no additional video delays or other processing necessary upon
decoding of the data stream, since the audio will be in sync once decoded. This method is
not recommended if the source program will be edited prior to decoding of the Dolby E
data stream.
In the case of Dolby E with high-definition video, HD video machines have built-in
means of compensating for the one-frame Dolby E encoding delay. Upon playback of
the HD tape, the video processing built into the unit compensates for the one-frame
Dolby E decoding delay, thereby maintaining sync with the picture during editing and
upon decoding of the Dolby E data stream.
How do I compensate for encoding delays and decoding latencies when
authoring a Dolby Digital data stream for DVD?
A Dolby Digital data stream can carry time stamp information within each Dolby Digital
synchronization frame. These time stamps originate from the master timecode referenced
to the video content. When a DVD is authored, the authoring system looks at the time
stamps encoded within the Dolby Digital data stream and matches the timecode numbers
between the audio and video components.
When mastering a Dolby Digital data stream for DVD, be sure to include the appropriate
timecode signal to maintain sync with picture within the authoring system.
Does Dolby E replace Dolby Digital?
No. Dolby E is an encoding technology used only for professional distribution of
audio, such as from television networks to affiliates through satellite communication
or via hard media like digital videocassettes. Dolby E is specifically designed to allow
numerous generations of encode/decode cycles that are sometimes necessary for the
production and distribution of audio in a broadcast environment. Dolby Digital is
designed to deliver digital audio to the home through digital television broadcast,
DVD, or other media. As it is optimized for high quality at low data rates, Dolby
Digital encoding should be performed after all final production decisions have been
made and the next decode step would be in the consumer’s home.
(123 pages)
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