ffmpeg intermediate transcode for 1920 x 1080 8-bit YUV 4:2:0 @ 25fps source

Question

I have a bunch of footage shot on a Canon 7d I'd like to transcode for editing in Davinci Resolve (I'm exploring alternatives to using Resolve's proxies).

The source footage is 1920x1080 8-bit YUV 4:2:0 @ 25fps.

I'd like to use ffmpeg and either the DNxHD or DNxHR encoders but DNxHD doesn't appear to have a matching profile and errors our and DNxHR outputs 4:2:2 video (which is arguably unecessary in this case) and doubles the original file size.

DNxHR

ffmpeg -i "input.mov" -c:v dnxhd  -profile:v dnxhr_sq -pix_fmt yuv422p -c:a pcm_s16le "output.mxf"

DNxHD (errors "maybe incorrect parameters")

ffmpeg.exe  -i "input.mov" -vcodec dnxhd "input.mxf"

My questions are as follows:

1. Are either DNxHD or DNxHR capable of outputing to 4:2:0? Would doing so keep file sizes down?
2. Can DNxHD transcode my source? If yes, how should I ammend the above ffmpeg parameters?

Answer 1

1. Are either DNxHD or DNxHR capable of outputing to 4:2:0?

No. Running ffmpeg -h encoder=dnxhd will list encoder properties, including

Supported pixel formats: yuv422p yuv422p10le yuv444p10le gbrp10le

2. Can DNxHD transcode my source? If yes, how should I ammend the above ffmpeg parameters?

The DNxHD encoder only supports a limited number of preset profiles. Each profile is specified of a frame size, interlacing mode, bitrate and pixel format (which also includes chroma sampling scheme).

FFmpeg will automatically convert the input to a matching pixel format, but the rest has to be manually set.

So, for a 1920x1080 8-bit YUV 4:2:0 @ 25fps source,

ffmpeg.exe  -i "input.mov" -c:v dnxhd -b:v 115M "input.mxf"

Try to encode with a non-matching to prompt an error message with the list of supported profiles.