Okay, I think I’ve narrowed it down further and found the problem, in my case at least.
When you encode to H264 format, you can choose to output as “Closed GOP” or “Open GOP”. GOP stands for “Group of Pictures” and it’s something to do with the way that various compression frames are arranged. Something like that… it’s too technical for me!
As I understood it, “Closed GOP” files are meant to be used when you know you later want to edit the file, and then when you’re ready to output the final version, you use Open GOP. So all my re-encodes were done with “Open GOP”. These are the ones failing.
I can take a native MPEG-2 DVD rip of a title and encode it using the exact same H264 encoding settiings: one with “Open GOP” and the other “Closed GOP”. Every time, the reencoded file with “Open GOP” throws up the error; the other doesn’t.
What I think might be happening is that with Closed GOP, the video preview thumbnail generator assumes it can read a set number of frames and then encode them. In files encoded with Open GOP, I think the frames aren’t following the “correct” order, which is why the error says it expected x number of frames but didn’t get them.
That might explain why “REMUX” files have this problem: often they’re re-encoded from the original to be smaller, and they might use Open GOP.
EDIT: Looking at the text file posted by f18cc above about a remuxed file that didn’t work, it includes “open_gop=1” in the encoding settings…
Devs! Is there any way you could detect if a file uses Open GOP encoding, and alter the behaviour of the thumbnail generator if it is?
