Q100228: Understanding the bit rate of Avid DNxHD Codecs
This article outlines how to choose between the different bit rates for exporting Avid DNxHD Codec .mov files in Nuke.
Nuke only supports a set range of DNxHD codecs, list that can be found in our Nuke Online Help here. 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 the Nuke Online Help 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.
Conclusion: if you read through the Nuke Online Help data sheet until you find your desired bitrate, then the number on the left of the data sheet is the number you should choose in the codec profile list in Nuke.
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