I imported around 1300 m4v files into Subler to batch Optimize them. They're a mixture of remuxed mkvs from iFlicks and converted avi's from Handbrake. 281 of the 1300 won't Optimize - Subler just immediately puts a red Stop sign next to them and moves on to the next file. What's weird is it's a mixture of files that won't optimize - some remuxed mkv's, some converted avi's. For example, I have the whole of season 23 of the Simpsons, every episode obtained from the same source. All episodes up to and including 12 optimised just fine in Subler, but 13 onwards won't.