TIFFs are similar in quality to DNGs. I don't have any experience with the Windows version of MLV App.
Are you exporting TIFFs from MLV App or are you converting to TIFFs in ffmpeg?
In regards to your syntax error, your path to the TIFF file has a space in the directory name "/very beautiful/", and that space might not be parsing properly. When you type/enter that path, an escape character such as a back slash ("\") might be required just before the space, so that it reads "/home/meerkat/Videos/very\ beautiful/M20-2351/M20-2351_000000.tif"
However, the simplest fix to that path space might be merely to rename the "/very beautiful/" directory to "/very_beautiful/".