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DNX HD Codecs? What’s the real story?
Hopefully, someone can help me sort out some confusion I’m having re: the DNX codecs.
I recently performed my first edit session on an Adrenaline-HD system (v2.21). When I opened Media Composer and created a 1080i, 29.97 project – the available DNX codecs were (to the best of my recollection):
DNX-245-x
DNX-245
DNX-220
DNX-180
DNX-145My question is this: Avid’s website makes no mention of DNX-245 or DNX-180 for that matter, yet – when going back over my notes from that edit session, I wrote down that I used DNX-180 for my ingest and rendering codec. Am I going nuts or are there codecs in V2.21 that aren’t even referred to on Avid’s website??? I don’t have access to the MCA-HD that I used a couple of weeks ago, so I can’t verify this!
Michael Buday
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3 Replies
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Michael,
It could be that Avid’s done some tweaking on the codecs, but basically the number used in the codec name is based on the data rate “family” and then varies by the frame rate of the project. This description is from Avid’s chart:
“Avid DNxHD is available in three HD encoding choices per resolution/frame rate combination, each identified by bandwidth (megabits/second) and bit depth. At 59.94 frame rates the choices are Avid DNxHD 220x 10-bit, Avid DNxHD 220 8-bit, and Avid DNxHD 145 8-bit. The names designate the bit rate, with “x” designating 10-bit. For example, a 1920x1080i/59.94 HD raster captured as DNxHD 220x requires 220 megabits/second, whereas 1280x720p/23.976 captured as DNxHD 90x requires only 88 megabits/second to achieve the same high image quality as its source. The following chart details available resolutions for Media Composer Adrenaline HD.”
So according to Avid’s chart, 1080i/59.94 at the resolution of DNxHD 220x is the same amount of compression per frame (917504 Byte/F) as 1080p/23.976 at the resolution of DNxHD DNxHD 175x (917504 Byte/F).
Clear as mud, right?!
Sincerely,
OliverOliver Peters
Post-Production & Interactive Media
Orlando, FL
http://www.oliverpeters.com -
Thanks Oliver, but you’re right – I’m still confused! I think they have done some tweaking on the codec names ’cause I could swear that I saw 245mb/s and 180mb/s codecs on the MCA-HD I was using.
All the best,
Michael
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Michael,
You may be right. The way I understand it is that there are 3 basic compression rates. 10-bit at 6:1, 8-bit at 4:1 and 8-bit at 7:1. The variations of these times the various frame rates gives you the DNxHD numbers based on the resultant bandwidth.
Sincerely,
OliverOliver Peters
Post-Production & Interactive Media
Orlando, FL
http://www.oliverpeters.com
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