FCP X does all of this for you.
1. Import media and create proxy media.
2. Set playback preferences: CHECK USE PROXY MEDIA
3. Edit
4. WHen you are done go into playback settings and CHECK USE ORIGINAL HIGH QUALITY MEDIA
5. Set your Sequence to PRORES 4:2:2 HQ
6. Final Cut Pro X now renders out your edit with the original media to the Prores Codec giving you the best quality.
It’s so simple most people don’t want to believe it is true, but it really is that easy.
David
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The shortest answer is doing.
Lord Herbert
https://vimeo.com/battistella