OK! So, just thought I'd update here with my findings after experimenting a bit more.
This problem is almost certainly introduced at some point in the m4v remuxing/tagging process. My process for mkv files is as follows: use mp4tools to remux into an m4v, then drop into Subler and tag them. I originally thought this issue was limited to 1080p content, but I discovered today that a 720p file (tv ep, ripped from a blu-ray, roughly ~3GB) did the juddering after something like 5+ minutes of playback. This happened on something like three episodes in a row (watched in a marathon), so I had to resort to the old 'tap the back arrow, then hit play' to eliminate it for another 5 or so minutes.
Despite having created this m4v with the latest version of mp4tools in the first place, running it through the 'remux' only option in the 'Edit' pane resolved the problem. So either mp4tools isn't doing this initially, which is unlikely, or Subler is breaking the files somehow. Regardless, the 'Remux' process in mp4tools available in the Edit pane retains the tags, so the file is identical but doesn't stutter on motion after a few minutes of playback. My files typically have AC-3 5.1, AAC 2.0 *and* DTS audio in them, and since adding this final remux step to my workflow, the problem is gone. I've watched another two or three episodes since and this show has plenty of motion, so I'd definitely have noticed it if it was.
Obviously it would be nice if I didn't have to do this extra step, so I'm holding out hope that the new Apple TV software counterpart to iOS 8 resolves it. Regardless, this is a consistent solution for me.
Apologies if you knew all this already, but both myself and a few others here appeared to be uncertain as to what was at fault here. I can pretty conclusively rule out, at least for my part, stuff like VBR audio, file size or resolution.
This problem is almost certainly introduced at some point in the m4v remuxing/tagging process. My process for mkv files is as follows: use mp4tools to remux into an m4v, then drop into Subler and tag them. I originally thought this issue was limited to 1080p content, but I discovered today that a 720p file (tv ep, ripped from a blu-ray, roughly ~3GB) did the juddering after something like 5+ minutes of playback. This happened on something like three episodes in a row (watched in a marathon), so I had to resort to the old 'tap the back arrow, then hit play' to eliminate it for another 5 or so minutes.
Despite having created this m4v with the latest version of mp4tools in the first place, running it through the 'remux' only option in the 'Edit' pane resolved the problem. So either mp4tools isn't doing this initially, which is unlikely, or Subler is breaking the files somehow. Regardless, the 'Remux' process in mp4tools available in the Edit pane retains the tags, so the file is identical but doesn't stutter on motion after a few minutes of playback. My files typically have AC-3 5.1, AAC 2.0 *and* DTS audio in them, and since adding this final remux step to my workflow, the problem is gone. I've watched another two or three episodes since and this show has plenty of motion, so I'd definitely have noticed it if it was.
Obviously it would be nice if I didn't have to do this extra step, so I'm holding out hope that the new Apple TV software counterpart to iOS 8 resolves it. Regardless, this is a consistent solution for me.
Apologies if you knew all this already, but both myself and a few others here appeared to be uncertain as to what was at fault here. I can pretty conclusively rule out, at least for my part, stuff like VBR audio, file size or resolution.
