analogue composite to hdmi and lock signal

[G4WIM]

Hi guys, yet another question.

This is one I've solved in the past but have lost the 'recipe'.

I need to convert an analogue video signal from a FM rx to HDMI and generate a lock / signal present signal.

In the past I think I used an LM1881 plus 567 PLL chip for the lock signal.

Now perhaps I should use a RPI plus a usb video dongle for the conversion and some external signal detection for the lock signal.

I do have a cheap composite to HDMI converter but yet to determine how well it works with a noisy signal but would still need to generate a reliable lock signal.

Any comments / ideas ?

Regards Tim