Although FCP’s Media Manager function was pretty dicey in the past (it was commonly called the “Media Mangler”) it achieved ‘reliable’ status by the time FCP 7 came out. It does still have some limitations though. For one, you can’t change frame rates. Not sure why but you just can’t. Another thing is that if you are transcoding the footage you are limited to using a list sourced from FCP’s sequence presets. Normally this is fine because all the typical codecs you work with are there in a variety of permutations. From DV to Uncompressed to DVCPro HD to ProRes (of course).
But what if you want to transcode into something that isn’t on the list? Something like Avid’s DNxHD? Hmmm. The solution is actually pretty simple.
All you have to do is go into the FCP drop down menu, select Audio/Video settings, click on the Sequence Presets tab and make a new preset with whatever settings you want (keep in mind the frame rate limitation still applies). Then go into the Media Manager and your custom preset will appear in the drop down menu for recompressing options.