[Thalyn]

That all being the case, I think I have a new hypothesis as to what's happening; again using John Carter as reference.

I'm wondering if there's some kind of plane "hierarchy" where those frames defined as 0x80 (effectively nothing) actually use a different plane to source their information from. Using TMT to double-check for the correct offsets I have determined that subs 29 and 30 of track 10 have depths of 1 and 6 respectively. Using the frame numbers from your earlier post the assigned plane 7 has those locations as entirely 0x80, but if I check the other files I find a 1 and 6 present at what appears to be an appropriate location in plane 1 (no other planes have these values nearby). Plane 1 is used for subtitle track 9, which is the one right before the one I'm using.

In saying that, the frame numbers don't exactly match up - the movie frame is before the offset I'm checking by 52 frames. I'm taken to believe there's actually a small delay at the beginning of most streams used in video to allow for syncing which could explain the offset. My napkin math doesn't quite match up with your tool either so there's obviously a discrepancy I'm not taking into consideration, so that could be expected (napkin math puts the difference at 63-64 frames depending on rounding). The 0x06 entries start at offset 49743 in the plane file while TMT shows sub #29 changing depth at the very end.

The question is whether this hierarchy is simply a case of "If not found, use previous track's plane (and keep going back as necessary)" or "If not found, use pre-designated plane" - answering which would require more knowledge of how the MPLS structure works than I have. I'm inclined to believe it's simply a "previous track" deal myself but I have nothing over a gut feeling to back that up. Both seem wasteful since 0x80 takes as much storage space as the correct value, unless the planes are compressed using a system like RLE8 in which case it would be slightly more storage efficient.

This may also be what's indicated by a "zerro" plane - one which simply references another in its entirety, in the event it doesn't actually mean "all zeros". Though why it isn't just assigned to the other plane directly is again confusing.

Unrelated, I don't recommend TMT for 3D playback. At least, not if you have a passive screen - it produces the same aliasing I observed when simply taking alternating scanlines for each stream, yielding a watchable-but-slightly-unpleasant result.

*ed: A simpler but possibly still correct way for these 0x80 subs to get a depth could be just a simple plane "stack". JC, for example, has 10 subtitle tracks with the one I'm wanting to use conveniently being the last. To get the final depths it could just load all the depths starting from the first subtitle track and ending with the requested one, overwriting the depths as it goes with 0x80 meaning "keep the existing value". As such it would load (in order) plane 8, 0, 5, 9, 2, 3, 6, 4, 1 and then 7. It seems wasteful and inconvenient, but so is having undefined depths to begin with.