I am not capturing anything, I did a log and transfer, they are hvx 720p 24PN files
I can take them to AE via reference movie but I just dont know how to bring them back, which codec to use, I can either use the animation, or uncompressed and both of those are gonna be heavy
If you want absolutely no loss, use animation, uncompressed.
If you want something that no one will ever tell the difference of, use ProRez.
If you don't care and don't want to render again in FCP, export at DVCproHD. If you are making DVDs and such, no one will tell.
If you are using AE CS3, make sure to go into your project settings and disable AE's stupid Color Profiling (Use Legacy Settings check box) or all your footage will be about 10% darker in FCP, thanks to some awesome metadata switch that the new CS3 turns on.
He suggests that basically you take your footage in Final Cut, and look at the waveform. If anything is over 100 IRE, you should lower its levels (you set a layer of black below the video, then turn down the video's opacity a bit until the levels are 100IRE or below). Now you've preserved your superwhite values.
In Sequence-->Settings, change the checkbox to say "Render in best YUV" or something like that (the bottom button). Now you're in 32 bit float, so maximum color range is preserved.
Then export a Quicktime, but don't use a preset, just say "custom" and change it to Uncompressed 10 bit (don't use the preset one or your HD will be resized to SD). These are BIG files, but are lossless and preserve all of your highlight data etc.
Send them back to FCP from AE using this same uncompressed setup and you will cut your losses. Hope that makes good sense...