Yes I can just transfer the files manually from the internal storage (to which the Sony app writes them) to the ext SD card.
The issue would be if the internal flash storage doesn't have enough room. For example my 16GB T705 has only 8GB room internally, but 38GB on the extSDcard, and the latter can probably go to 128GB size (has anyone tested that?). Potentially I might want to transfer the whole 64GB camera card to the tablet, for editing.
Given the FDR-1000V camera, from which I need to move the videos, stores in max 4GB chunks (FAT32) on its SD card (currently this is 64GB) I could move one chunk at a time, maybe, just about, from the internal memory (8GB room) to the ext SD card.
But even then I need a video editor which can work on a user-specified folder (on the ext SD card) - any suggestions? (I need only simple functions: cutting stuff out, 180 deg inversion).
I can see the "usability committee" working here... we get the same under Windows where the Documents and Settings has been used to dump pics and videos as a default location for years, resulting in 90% of people not caring and being happy and 10% tearing their hair out because they can't find the stuff about five levels of directories below... The problem is that on a PC you have loads of storage whereas with a 16GB tablet the default storage locations are limited, and if some stupid people in Sony Marketing hard-code the app to use only that... and this is despite everybody knowing the camera they sell can hold 64GB whereas almost no client device has enough room!
FWIW, I think that the Sony app obtains the default path /storage/emulated/0/movies via the android API and not by it being hard coded. If it is the latter then any attempt to move the default location will obviously not work.