I understand that some (most?) deinterlacers convert from interlaced to progressive at the same frame rate, eg from 50i to 25p. What method is considered to give the best quality when converting interlaced to double frame rate progressive, with up to double video bit rate if need be?
Use the Bob deinterlace in Handbrake.
Note that that tutorial is very old and I'm actually in the midst of updating my method and plugins this very month. If you're in a hurry then you would still be able to get going by following the tutorial as it is. Replace the dependencies in the "February" list at the top with any of the same plugins by pinterf from here. And you might consider using his AviSynth+ build instead of SEt's AviSynth 2.6 MT, but that entails some required changes to your AVS scripts. Also, if you want AVI intermediate or final renders rather than MP4 then you'd render with VirtualDub, not MeGUI. If you want to Frameserve then use 32-bit versions of everything. If you're happy to go via an intermediate then you can try 64-bit versions.
Also bear in mind that the new Smart Adaptive Deinterlacing in VP14 is pretty good, but I haven't tested if its goodness will also translate to a double-frame-rate render.
You can install too this free plugin: Yadif Deinterlace.I get many satisfaction wit it.
50i to 50p the best way involves a special filter, called "Bob."
Versions of the Bob filter are available in Avisynth, VirtualDub, and other command line encoders. An advanced Bob Deinterlace filter is built into Handbrake GUI, and it is quicker than some command line methods.
The 2x equivalent in Yadif plugin may be good enough, depending on source motion.
Thanks for the replies. I will look into the suggestions and see what works best for me.