I'm wondering: What is the best way to preserve the quality of my AVCHD-based timeline when exporting as Blu-Ray-compatible H.264? My feeble understanding of AVCHD is that it *is* H.264, which would suggest that very little transcoding would be required to make it ready for Blu-Ray. However, Adobe Media Encoder always requires you to choose a quality, bitrate, etc., which has me thinking that it will always recompress. I don't see any "leave it alone if possible" option.
You are right Adobe Media Encoder does not provide any "leave it alone if possible" kind of option.
But to preserve the quality of the source AVCHD one could do the following.
1.Keep the value of bitrate high (as already pointed out by you).
2.Use VBR 2 pass encode.
3.Also if you notice on the "extreme right" of the AME settings window next to the video,audio etc tabs there is a flyout menu,if one clicks on that one gets an option of "Use Maximum render Quality"
using that will also help preserve the quality of the source.
please mind that all of the above are costly operations in terms of time.