I chose the Hauppauge USB-Live2 to perform the analogue to digital conversion, and have been very happy with the results.
The command I used for the capture was:
mythffmpeg -y -loglevel debug -f alsa -i plughw:1,0 -f v4l2 -s pal -pix_fmt yuyv422 -i /dev/video0 -b:v 2048k myfile.nut
on a Mythbuntu 14.04 system, although it should be easily adaptable to other installations, e.g. using ffmpeg instead of mythffmpeg.
The components of the command that may need to be changed:
The Audio input device (plughw:1,0): On my system, executing:
> arecord -l
**** List of CAPTURE Hardware Devices ****
card 0: Intel [HDA Intel], device 0: AD1981 Analog [AD1981 Analog]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 1: Cx231xxAudio [Cx231xx Audio], device 0: Cx231xx Audio [Conexant cx231xx Capture]
Subdevices: 1/1
Subdevice #0: subdevice #0
Shows that the Live2 (which uses the Cx231xx drivers) is card 1, subdevice 0. And:
> arecord -L
[... removed irrelevant entries ...]
default:CARD=Cx231xxAudio
Cx231xx Audio, Conexant cx231xx Capture
Default Audio Device
sysdefault:CARD=Cx231xxAudio
Cx231xx Audio, Conexant cx231xx Capture
Default Audio Device
dmix:CARD=Cx231xxAudio,DEV=0
Cx231xx Audio, Conexant cx231xx Capture
Direct sample mixing device
dsnoop:CARD=Cx231xxAudio,DEV=0
Cx231xx Audio, Conexant cx231xx Capture
Direct sample snooping device
hw:CARD=Cx231xxAudio,DEV=0
Cx231xx Audio, Conexant cx231xx Capture
Direct hardware device without any conversions
plughw:CARD=Cx231xxAudio,DEV=0
Cx231xx Audio, Conexant cx231xx Capture
Hardware device with all software conversions
The video device (/dev/video0) can usually be guessed by looking at the output of ls /dev/video*. If there's only one video device, that's it, if there are two, the first is probably the built in webcam. If you really want to be sure, look in /var/log/syslog at the time you plugged the Live2 in:
Jan 28 14:30:49 myth kernel: [ 5319.874560] cx231xx #0: cx231xx #0/0: registered device video0 [v4l2]
Jan 28 14:30:49 myth kernel: [ 5319.874652] cx231xx #0: cx231xx #0/0: registered device vbi0
Jan 28 14:30:49 myth kernel: [ 5319.874656] cx231xx #0: V4L2 device registered as video0 and vbi0
The PC I used for transfer doesn't have a webcam, so it is video0, as confirmed in the syslog extract above.
-b:v 2048k specifies the bitrate to record at. 2048k is probably overkill, but I figured that I won't have another chance to capture the tapes, so a little extra disk space isn't worth worrying about.
After capturing the video I trimmed the blank video at the start and end, and fixed the timestamps using:
mythffmpeg -ss -t -fflags +genpts -i myfile.nut -vcodec copy -acodec copy myfile.mkv
Where x is the start offset in seconds, and y is the length of the video in seconds.
Some articles I've read have discussed capturing video simply using:
cat /dev/video0 > file.mpg
this won't work for the Live2 as it is a simple frame-grabber, and doesn't have onboard compression.
The only hiccup in the whole process is that the Live2 more reliable if it is plugged in to a USB port that is using the ehci stack. Newer computers that support USB3 and use the xhci stack will have problems. If you want to check, once again looking at /var/log/syslog:
Jan 28 14:30:45 myth kernel: [ 5316.076069] usb 1-6: new high-speed USB device number 3 using ehci-pci
Jan 28 14:30:45 myth kernel: [ 5316.210847] usb 1-6: New USB device found, idVendor=2040, idProduct=c200
Jan 28 14:30:45 myth kernel: [ 5316.210856] usb 1-6: New USB device strings: Mfr=1, Product=2, SerialNumber=3
Jan 28 14:30:45 myth kernel: [ 5316.210860] usb 1-6: Product: Hauppauge Device
Jan 28 14:30:45 myth kernel: [ 5316.210863] usb 1-6: Manufacturer: Hauppauge
From the first line above we can see that in this case the Live2 is using a ehci port.
[EDIT 11 APRIL 2015] Kernel 4.0-rc7 includes patches which largely resolve the issues with USB3 / xHCI ports and Intel xHCI controllers. More specifically, the problem was with Intel xHCI controllers and isochronous USB devices (i.e. video and audio capture devices). It looks like there are still some issues, however the current hypothesis is that they are issues to do with the cx231xx driver that are triggered by the differences between the eHCI and xHCI drivers. Depite these issues, if you have an Intel xHCI controller, cx231xx devices are now usable on USB3 ports, and other video / audio capture devices may well work without any problems. If you're interested in the details, please see: http://www.gossamer-threads.com/lists/linux/kernel/2126922
Many thanks to Devin Heitmueller, Mathias Nyman and Lu Baolu for their assistance it getting the Live2 working for me.
[EDIT 25 Apr 2015] More good news: The patch has been back-ported to 3.19.5, 3.14.39 and 3.10.75.
[EDIT 20 Jun 2015] More good news: Ubuntu kernel 3.19.0-21 (and a couple of earlier version, I think) are based on mainline 3.19.8, which include a few more fixes than mentioned above.