ImageMagick command

Looter, you can give one of these a try and see if they work for you. Ultimately you have to find the lowest common denominator that gives you something reasonable since different content providers using different encoding and post-edit techniques. There really isn't a one-size fits all.

In any case, try one of these, which I find does a reasonable job for the most part:

We use this on our Mechbunny TGP Script and it typically does the job, but we have some content providers with small "large" pics and they're already pretty sharp so it's a challenge. This one seemed to let us accommodate a wide assortment of content providers.:
We use this one with Arylia and it works quite nicely:
We use this one with the older JMBSoft TGP and it works nicely:
Again, there's no one-size fits all. Ultimately, some thumbs will look great and some not so much. And like I mentioned, the key is in finding a balance you can use for multiple content providers.

If all else fails, trial and error is your best teacher. The command line options are here:
ImageMagick: Command-line Processing

Good luck.

robwod,

Thank you. Yes, I have spent countless hours/days on the ffmpeg testing and this. Learned a lot about ffmpeg but not much on imagemagick. Pretty close to what I am running now except adaptive-sharpen. I will run this on some of my content as soon as it's ftp'd.