So I just tried it out with both a 32gb and 64gb flash drive with an OTG microUSB adapter. The flash drive should be formatted as MSDOS FAT32.
You only need your iPhone - Mobile device to initially select the USB data transfer mode in the plugins in the camera settings (not the shooting settings). This setting is retained on the Theta.(It appears)
After you are done filming and want to do the transfer. Insert the OTG Flash drive. Hold the mode button until the camera status light turns white. Hold and release the shutter button and then the camera icon will flash while it transfers the files to the USB Flash drive. This takes a while,
Once the transfer is done, the camera returns back to regular shooting mode. (The white camera status light returns returns to blue.)
The files should now be on the flash drive and the original files deleted from the camera.
Excellent job, Ricoh!
Here is a quick YouTube video:
