Q100228: Understanding the bit rate of Avid DNxHD Codecs

Peter Coleman

Updated : March 12, 2024 21:20

Created : November 18, 2016 17:56

SUMMARY

This article outlines how to choose between the different bit rates for exporting Avid DNxHD Codec .mov files in Nuke.

MORE INFORMATION

Nuke only supports a set range of DNxHD codecs, list that can be found in the Supported File and Camera Formats of Nuke's online documentation. Using this information you can work out which codec profile to use for the file you want to write. 

In the help information you can find the formula to calculate the bandwidth for custom frame rates, and in the example below we are going to work out how to get a bitrate of 115 Mbit.

Here are the options you would see in the Write node:

Below is data taken from Nuke's online documentation on different bit rates you may use:

• 1080p/24 350x, 175x, 175, 115, 36 (same at 23.976)

In the case of 1920x1080 footage, using a frame rate of 24 fps or 23.976 fps with the DNxHD 422 8-bit 145Mbit will actually give you a 115Mbit file.

• 720p/50 N/A, 175x, 175, 115, N/A

At 1280x720 with a frame rate of 50 fps with the DNxHD 422 8-bit 145Mbit will actually give you a 115Mbit file.

In more recent versions on Avid, the DNxHD codecs now have new simplified names, as found in Avid's documentation here: https://resources.avid.com/SupportFiles/attach/WhatsNew_MediaComposer_v20.4.pdf

Below is a table of the old Avid names, used in the above conversion, the new names, and the option to use in your Nuke Write node with that resolution and framerate to get the desired DNxHD output.