I've just started converting a whole box of old tapes...
I have a little Elgato "EyeTV Hybrid" USB dongle that comes with SVideo, Composite, L/R audio, and antenna RF inputs. The EyeTV3 software allows live recording into MPEG-2 format with a couple (limited, but selectable) encoding rates. The "high (DVD 90 min)" setting gives 720x480, 29.97 fps, 6.0 MBS VBR (8 mbps max), IP frames with 48kHz audio at 384 kbps. It uses an AMD ATI Theater T507 demodulator / USB / Video controller and a NXP TDA18271C2 tuner chip for OTA HD TV reception if you have an antenna.
It also allows a "Live TV Buffer" feature that ues up to 1.5GB of RAM to off-set any recording lags due to disk I/O issues.
I haven't tried to see if FCPX or IMovie / IDVD will see the device and record directly. First tape will is being recorded using the EyeTV software just to kick the tires.
My deck is a consumer Philips VR960. nothing special... hooked up via SVideo and component audio.
recording on a 2011 MacBook Pro via USB2.
13 minutes == 725.4 MB recorded file.
Now being automatically exported into H.264 by the EyeTV software because I have the "Prepare all new recordings for iPhone/iPad" option checked in the preferences.
When it's done, I'll import the original recording into FCPX and see how it looks...