Here are some command that I use with ffmpeg when trying to transcode from my Canon DSLR H.264 movie files.
This is my favorite, H.264 to Prores HQ422
ffmpeg -i FILENAME.MP4 -c:v dnxhd -profile:v dnxhr_hq -pix_fmt yuv422p -c:a pcm_s16le FILENAME.mov
H.264 to Prores HQ 444
ffmpeg -i FILENAME.MP4 -c:v prores_ks -profile:v 4 -pix_fmt yuv444p10 FILENAME.mov
H.264 to DNXHQ 4222 (10-Bit)
ffmpeg -i MVI_0256.MP4 -c:v dnxhd -profile:v dnxhr_hq -pix_fmt yuv422p -c:a pcm_s16le BRYAN10.mov
Thank you for watching.