External Recording - ARRI ALEXA Series User Manual

Recording

12.1.2 External recording

Dual recording
The Dual recording function is only available on ALEXA Classic
cameras with an SxS module. It allows recording to two SxS PRO
cards in parallel, creating an instant backup at the time of recording. To
enable dual recording, set Dual recording to On in the INTERNAL menu
(in RECORDING menu).
Requirements for dual recording:
The SxS PRO cards must be of the same capacity.
When reloading, or changing reels, both cards must be
formatted.
The SxS PRO cards must have identical file structure.
Follow the procedures for normal recording to a single SxS PRO card,
but manage the SxS cards as a set. Download and back up one card
and keep the other card as an additional backup.
In addition to internal recording, the ALEXA can also output
uncompressed HD and unprocessed ARRIRAW* data to external
recorders over the REC OUT.
Choose the preferred output format based on the following basic
guidelines:
422 1.5G: use for television applications that require only color
correction and high-speed capture above 30 fps.
444 1.5G: Use for high-quality television applications that require
color correction and visual effects work such as pulling mattes,
and for cinema applications.
ARRIRAW*: Use for high-quality cinema applications destined
for multi-format distribution.
422 1.5G YCbCr
422 is a format in which color is sub-sampled, meaning that the
camera-native RGB image is transformed to a YCbCr color space. Y
represents luminance, while Cb and Cr are color difference signals. Cb
and Cr are sampled with only half the horizontal resolution, as the
human eye is less sensitive to color resolution than to luminance
resolution. 422 is a good balance of lower bandwidth in transmission
and high quality visual results.
For frame rates up to 30 fps, 422 1.5G is transmitted over a single HD-
SDI cable. REC OUT 1 and REC OUT 2 carry the identical signal
independently. When shooting frame rates higher than 30 fps, the
signal is split across both REC OUT 1 and REC OUT 2 and requires
connecting two HD-SDI cables.
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