[Seth Emmons]

Support for “video trigger” is an addition to the SMPTE specification for HD-SDI and has begun to be implemented by the camera manufacturers. External recorder manufacturers are also now supporting it.

This works by the camera inserting a bit sequence into the HD-SDI stream when the ‘REC’ button is pressed. When powered on, the recorder is constantly looking for it. When it is seen, the recorder activates.

For the Arri Alexa, the internal SxS recording and the external recorder will begin recording simultaneously. There is no ‘spin-up’ time lag, since all the devices are solid state and not using hard drives anymore for obvious reasons. This allows for what is known as DUAL RECORD functionality, in which the SxS card ProRes format becomes used for Dailies and the uncompressed external recorder (ARRIRAW or DPX) files are used for final finishing. It’s efficient, fast and delivers great quality.