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Old March 7th, 2006, 05:54 PM   #1
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How do they they get 1.485Gb/sec HD SDI

I keep seeing a data rate of 1.485Gb/sec for HD SDI 10-bit on all the capture card websites, but when I try to calculate it manually I get 1080x1920x60x10=1,244,160,000Mb/sec or 155.5MB/sec. I know I'm screwing something up in the calculation I'm just not sure what it is. Maybe I forgot to add some bitrate for 2 channel sound or something.

I'm configuring a dual-role fiber channel SAN storage system that acts like a standard business fiber SAN during the day (Servers, Oracle and SQL Server 2000) and a video capture fiber SAN by night. So the systems integrator asked what is the minimal sustained throughput you require for the heaviest sustained data transfering to SAN task. I figured that would have to be capturing HD SDI 10-bit direct to SAN disk from the HBA on the PC.

The other question I had is whether or not the realtime playback data-rate of uncompressed video increases (on the NLE timeline) as you add additional filters and effects etc. to the clip to be rendered in realtime?

I hope this wasn't answered before. I did search for 1.485Gb and didn't find anything.
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Old March 7th, 2006, 10:33 PM   #2
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Taken from: http://en.wikipedia.org/wiki/Serial_Digital_Interface
"The nominal 1.5 Gb/s interfaces support most high definition formats. Supported formats include 1080i60, 1080i59.94, 1080i50, 1080p30, 1080p29.97, 1080p25, 1080p24, 1080p23.98, 720p60, 720p59.94, and 720p50"
"The dual link HD interface supports 1080p60, 1080p59.94, and 1080p50, as well as 4:4:4 encoding, greater color depth, RGB encoding, alpha channels, and nonstandard resolutions"

the highest datarates are 60i and 30p at 4:2:2
just a guess, but...
10bits*((4+2+2)/4)=20bitsPerPixel
1080*1920*30fps*20bitsPerPixel = 1,244,160,000b/s
1244160000b/s / 1073741824b/Gb = 1.158Gb/s
This does not include other things that may make up the difference: stopbits, data protection, sound, etc. I'm probably way off on that, though.

If you're really curious, you could always pay the $30 to read the actual documentation for SMPTE 292M-1998: Bit-Serial Digital Interface for High Definition Television:
http://www.smpte.org/smpte_store/sta...CurrentPage=12
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Old March 8th, 2006, 08:37 AM   #3
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How about 1920 x 1080 x 30 fps = 62,208,000 data points per second, times 8 bits per color channel with three color channels (RGB) = 1,492,992,000 bits per second. Slightly less if you account for the actual frame rate of 29.97 fps.

Last edited by Kevin Shaw; March 8th, 2006 at 10:23 AM.
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Old March 8th, 2006, 10:05 AM   #4
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Numerologically Challenged!!

Quote:
Originally Posted by Alan Melling
If you're really curious, you could always pay the $30 to read the actual documentation for SMPTE 292M-1998: Bit-Serial Digital Interface for High Definition Television:
http://www.smpte.org/smpte_store/sta...CurrentPage=12
Alan I think your right that this 1.485Gb/sec is the official bit rate standard established by the SMPTE 292M-1998 for HD SDI. They probably take into account sound and other information that is defined and output to the HD SDI interface.
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