Nevion DWC-HD-DMUX - Manual (Page 11)

DWC-HD-DMUX Rev. F
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If a signal occurs that is more than ±6.8 µs (for HD, ±25 µs for SD) off relative to the “initial
phase signal”, the output will repeat the last frame, refill the buffer and take out data from
the centre of the buffer. This new signal is now considered the “initial phase signal”.
Hence, it produces an error free video output without frame wrapping when the video input
comes from a router with synchronous input video signals that all lies within ±6.8 µs (for
HD, ±25 µs for SD) of each other.
3.5 Scaling block
The Scaling block is the heart of the down-converter. The frame rate of the HD input
dictates the video standard that the Scaling block will produce: If the input is 50Hz-based,
e.g. 1080/25p, the output will be 576/50i, and if the input is 60Hz-based (with or without
pulldown), e.g. 720/59.94p or 1080/24p, the output will be 486/29.97i.
The following assumes that the aspect ratio of the incoming HD is 16:9, and that the
pictures are such that objects are shown geometrically correct on a 16:9 monitor. The user
must then set the crop and aspect ratio of the output and the illustration below shows the
options available. The figure assumes a 4:3 monitor that ignores the WideScreen
Signaling bits (WSS bits can be inserted automatically according to the selected aspect
ratio, or they can be turned off or replaced by a user selected value. See chapter 0 for
details.) Had the monitor in the example processed WSS bits, the full-frame picture in the
lower left would’ve been internally converted and shown letterboxed to preserve picture
geometry. The cropped edge 4:3 and letterboxed 16:9 options should normally only be
used for 4:3 monitor.
Figure 3: Picture cropping and geometry options
3.6 Frame synchronizer
The frame synchronizer consists of a frame store buffer and some control logic. The frame
store buffer can store up to 8 SD frames. When the input is an HD source to be converted
to SD, the frame synchronizer is placed after the Scaling block. When the input is SD, the