AJA KONA LHI, Инструкция по установке и эксплуатации

Страница: 21 / 86

1
15
KONA LHi Installation and Operation Manual — Understanding Typical
HDV
Data rate: 19 MB/second high definition720p, 25 MB/second high definition 1080i—
supported by internal system drive
Quality: Excellent
KONA LHi supports and accelerates the Final Cut Pro HDV Codec. You can use KONA LHi to
convert HDV projects to uncompressed—in real time—for monitoring and/or output.
KONA LHi can capture uncompressed from any input, directly to HDV media. The KONA
LHi advanced scaling engine takes the native frame (long GOP 1440 HD) and outputs it
via hardware—in real time. Precision AJA circuitry re-sizes the video to proper 1920 x
1080, providing quick playback of HDV captured by Final Cut for monitoring and
recording.
HDV captures HD images via MPEG2 compression and allows for recording the signal to a
MiniDV tape. This MPEG2 compression is similar to a DVD (although DVD is a program
stream vs. HDV’s transport stream and HDV uses a constant bit rate whereas DVDs use
variable bit rates). The issue for post production is that the HDV transport stream is based
around a long-GOP structure (group of pictures) which produces images based on
information over a section of time, via I, P and B frames; Intraframes, predicted frames and
bi-directional frames. Formats that do not use this scheme treat frames as individual
units, as in the progressive formats where a frame truly is a frame, or as interlaced frames
where two fields create the image. Sometimes we refer to these formats in contrast to
MPEG formats, as I-frame formats where frames can be easily defined as individual.
Since the frames of HDV have the long GOP structure to define them, herein lies the
problem for post-production; how can we work with the material if we must know what
lies before, after and during? Luckily, the transport stream MPEG2 can be transmitted
over IEEE1394 (aka FireWire). This means that the compressed HD material can be
transferred into systems with the appropriate hardware and software (for example, a Mac
Pro with Final Cut Studio 2). While this seems like a simple solution for post-production,
it means that the footage must be brought into the system as a rather heavily
compressed format and that the computer must continue to work with the material as a
MPEG2 transport stream, which is incredibly processor intensive for the computer.
How does the AJA KONA LHi card connect to HDV and digitize material to uncompressed
HD files for editing—or at the very least, to a lightly compressed I-Frame HD format? The
answer to this is provided in a feature common to many HDV devices: analog HD output
via component video. The component connectors on JVC cameras and decks, along with
Sony cameras and decks, allows for the output of the long GOP MPEG2 data as a standard
HD video format such as 720P in the JVC products—or 1080i in the Sony products.
Since the KONA LHi has the ability to digitize analog HD signals, the analog component
output of the HDV devices can simply be connected to the KONA inputs. Note that HD
signal cannot be transported over composite or S-Video (Y/C) cables, so the HDV device
must have an analog component HD output. The KONA LHi also has the ability to ingest
analog audio, so the analog audio outputs of the HDV devices can be sent to the Kona
card as well. (Also note that these analog audio outputs on the HDV devices are usually
unbalanced RCA connections where the KONA card uses balanced XLR style connection
so some sort of audio level correction device, such as a mixer or a stand alone active
interface amplifier, should be used for accurately attenuated audio.)
Finally, you will want to control your device. Where all of the video, audio and timecode
information moved over the FireWire cable, now you are dividing those tasks. Device
control is the most difficult to configure for HDV devices because so few HDV devices
have implemented any form of device control other than IEEE1394. The one notable
exception is the JVC BR-HD50 HDV deck which has a remote serial port for RS422 protocol
and device control. Check the KONA LHi support area on the AJA website for a
whitepaper on HDV, which gives details on using KONA LHi with various HDV equipment.
Note: direct capture into HDV media on the LHi is not possible. Direct capture into the
LHi can only be done using uncompressed, DVCPRO HD, or Pro Res. Regarding ProRes
422, capturing HD resolution ProRes 422 from an HD source requires a Mac Pro with
an Intel Xeon processor.