360 Systems MAXX, Руководство по эксплуатации

Страница: 88 / 137

86 System Configuration
Bit-for-Bit
®
Recording & Playback
The recording, storage and playback of audio program material such as Dolby®-E, Dolby
Digital (AC-3) or DTS® requires that upon playout the data stream be identical to the original.
Do not use the audio sample rate converters when working with these encoded audio formats.
The Image Server and a Dolby® encoder must be supplied with the same genlock signal.
Audio Sync Reference
The audio sample rate is derived from the selected video sync reference. Audio is recorded at a
nominal 48K sample rate, so the 0.1% pull-down for 29.97 NTSC is taken into account when
generating the audio sample rate for color NTSC. There is no drop frame in PAL video.
Time Code Source
This function selects the time code source for newly recorded clips. A time code value is
obtained from the selected input source at the start of a new recording. Choose VITC, LTC or
Manual input source. For manual, enter the desired time value for the first frame of the
recording in the Starting Time Code entry field.
MPEG-2 Profiles
Select either Main Profile @ Main Level (4:2:0), or 4:2:2 Profile@ Main Level for recording.
GOP Structure
GOP structure defines the MPEG Group of Pictures coding as combinations of I, P, and B
frames. The allowable combinations are presented in a drop-down list. I-Frame only encoding
will produce the least compressed picture and requires more hard disk space. However, I-
frames facilitate frame-accurate editing. For broadcast-quality resolution, I-frame encoding
should be considered at 25 Mb/sec and above. Low bit rates should never be used with I-frame
encoding.
Long-GOP video recorded with P and B frames produces superior image quality for a given
data rate, compared to I-frame. Most broadcasters go to air with 8, 10 or 12 Mb/sec content,
having long GOP length.
Encode Mode
Image Servers employ Variable Bit Rate (VBR) MPEG-2 encoding. For almost all broadcast
applications, VBR encoding produces superior results than its alternative, Constant Bit Rate.
Maximum Bit Rates
The range of available bit rates depends upon the MPEG-2 profile selected. In Main Profile @
Main Level, the record bit rate extends to 15 Mb/sec. In 4:2:2 Profile, the range extends to 50
Mb/sec.