Just an FYI, maybe this will help others.

I was trying to Demux a file and kept getting Failed in ffmepg Progress. Looking at the Info on the failed demux I saw that it kept saying Permission denied. Permissions onmy startup volume are fine BTW.

I had this file on a partition other than my OSX startup. In Get Info the disk even was checked to Ignore Ownership on the volume. I went to the folder I had my files in and Permissions were set to Owner:Me R/W, Group:Unknown Read only, Others: Read Only.

I changed the Read only's to Read Write and applied to enclosed items. I was then able to Demux the file. Well the Demux finished but came out bad, but that's a different problem, at least it demuxed and didn't fail.

Looking back at some logs I'm wondering if this hasn't been a source of other problems with ffmpegX, like only .m1v files getting created when Encoding, no final mpg.