Sound Devices PIX 250i - Manual (Page 30)

PIX 250i User Guide
v. 2.10 Features and specifications are subject to change. Visit www.sounddevices.com for the latest documentation.
24
Recor
ding
Progressive Segmented Frames (PsF)
Some cameras output video signal in progressive segmented frames (PsF). PsF is a method for
transmitting progressive video in an interlaced stream. A device generates PsF signal by splitting
each frame into two segments. PsF segments are the same as interlaced fields in that one segment
represents the even lines of a frame and the other segment represents the odd lines of a frame. PsF
segments differ from interlaced fields in that there is no motion between each segment in a pair.
The PIX 250i will automatically sense PsF signal from most cameras that output PsF over SDI. This
is accomplished through the use of a flag inserted into the SDI signal by the camera. If a camera does
not insert this flag into the SDI stream or if it outputs PsF signal over HDMI, then the Setup Menu
option [Video - Input PsF Detect] can be set to Interpret 1080i as PsF. This will force the PIX 250i to
treat all 1080i signal as if it were PsF and deinterlace it accordingly.
Selecting a Video Codec
Setup Menu option: [Video - Codec].
The PIX 250i has two families of intra-frame, DCT-based codecs available: Apple ProRes and Avid
DNxHD, with five levels of compression for ProRes and four levels of data compression available for
DNxHD. Both codecs are intermediate codecs that assist the editing process by eliminating the need
to transcode video before importing into Final Cut (ProRes) or Avid (ProRes or DNxHD).
ProRes is a variable data rate codec and DNxHD is a fixed data rate codec. PIX 250i supports all
compression levels and bit rates of ProRes and DNxHD and automatically records the correct bit rate
dependent upon the video input resolutions and frame rate. The data rates indicated in the Setup
Menu item [Video - Codec] indicate the maximum data rate at 1080p30.
DNxHD 36 Mb/s only supports 1080p signal. Standard definition recording is only available for ProRes
422 HQ, ProRes 422, and ProRes 422 Proxy.
Interruption of Signal During Recording
In the event that video signal is lost (an unplugged HDMI or SDI cable, for example) during record-
ing, the PIX 250i will pause the recording and wait for video signal to be re-initialized. If video signal
is re-initialized, recording will begin again to a new file of the same name with an “A” appended to
the end. Further interruptions of signal during that take will cause an alphabetic filename progres-
sion (“B”, “C”, etc).
Alignment of Audio and Video
An advantage to recording audio on the PIX 250i along with the video is the elimination of audio/
video sync problems in post. The PIX 250i has many options regarding audio sources along with the
two options for video inputs, HDMI and SDI. Given this flexibility, care must still be taken to ensure
good audio/video sync.
If recording camera audio embedded on HDMI or SDI, then the audio/video alignment will be ex-
cellent provided the alignment is proper on the camera.
If recording audio using the dedicated audio inputs (Analog or AES), then a delay may need to be
dialed in. The reason for this is that some cameras have a delay of one or more frames from lens to
SDI/HDMI output. The PIX 250i on the other hand has no appreciable delay between audio and
video. This means that if the camera does have this delay, the audio will lead the video as recorded
by the PIX 250i. Note that on some cameras, the lens-to-SDI/HDMI delay changes with resolution/