Is Blu-ray 3D BDXL?

This is weird, and I don’t yet quite know what to make of it. As I mentioned, I’m looking at the Panasonic 3D TV and its Blu-ray 3D player. With the TV you get two freebie Blu-ray discs: Coraline and Ice Age 3: Dawn of the Dinosaurs.

Note, this is a proper 3D Coraline using the sequential frame method to show different images to different eyes. Things are confused by the earlier Coraline discs which carry an anagylph 3D version (ie. using coloured glasses). That version works, but the colour range is very restricted.

Now for the weirdness. I thought I’d do a Blog post on how the files are structured on a Blu-ray 3D disc. It was doing this I noticed something very odd.

On a regular Blu-ray disc the content files are held in a folder BDMV\STREAM. Here are the first few from this disc:

 Directory of E:\BDMV\STREAM

30/03/2010  12:40 am    10,503,985,152 00001.m2ts
30/03/2010  12:40 am     5,199,513,600 00002.m2ts
30/03/2010  12:40 am    17,915,559,936 00003.m2ts
30/03/2010  12:40 am     8,772,323,328 00004.m2ts
30/03/2010  12:40 am        97,308,672 00005.m2ts

On a Blu-ray 3D, the 3D content is contained within a subfolder of the BDMV/STREAM folder, called SSIF. Here is the full contents from this disc:

 Directory of E:\BDMV\STREAM\SSIF

30/03/2010  12:40 am    15,703,498,752 00001.ssif
30/03/2010  12:40 am    26,687,883,264 00003.ssif
30/03/2010  12:40 am         1,032,192 00032.ssif
30/03/2010  12:40 am            61,440 00034.ssif
30/03/2010  12:40 am     1,002,817,536 00037.ssif

Now those are mighty big file sizes of course, but even a rough estimate of their total has them adding up to 85,000,000,000 bytes. In fact, according to the DOS DIR /S command, the total contents of the disc add up to 88,187,945,799 bytes. As I later discovered, BDInfo also gives this figure.

This is bit of a problem because the maximum capacity of a dual layer Blu-ray is 50,050,629,632 bytes.

Windows reports 46.6GB. But when I look at the ‘Properties’, it reports 50,050,629,632 bytes, which is the maximum capacity of a dual layer BD down to the last byte. That would make sense, since there is no reason why my computer’s Blu-ray drive would read more than two layers (both BDInfo and the DIR /S command work by toting up the sizes of all the individual files on the disc, as read from the directory index on the disc).

So what we appear to have here is one of two things. Either this is a super capacity Blu-ray disc carrying 82GB of data, or it is playing silly buggers with folder and file structures and indexes for some reason which is by no means clear.

The other day the Blu-ray Disc Association approved a new BDXL format, which offers 100GB in three layers and 128GB in four layers. This disc would nicely fit into three.

It would make sense for this new format to be introduced in conjunction with Blu-ray 3D, which also requires hardware changes. But I haven’t heard that this is actually happening.

Update (10:30am): The version of Ice Age 3: Dawn of the Dinosaurs included with the TV (disc name ICEAGE3_3DBUNDLE_F2) apparently has a size of 75,678,512,103 bytes, or 70.5GB.

Update 2 (10:47am): The answer to the question posed in the title is: No. In fact, it turns out, that my alternative explanation is correct: ‘it is playing silly buggers with folder and file structures and indexes’.

This post over the the Unofficial Blu-ray Specs Thread gives the answer:

It’s actually 38.68 GB total of “real” data, the SSIF folder (Stereoscopic Interleaved File) is a virtual folder created by combining files in the normal stream folder. 00004.m2ts is the left-eye stream, with normal AVC encoding, nothing out of the ordinary. 00005.m2ts is the right-eye stream with the 3D extensions, using MVC encoding (Multiview Video Coding). They combine, or interleave, to create the virtual 32.7 GB 00004.ssif file in the SSIF folder, which is the actual 3D version of the movie. The file system layer enables a set of files to share the same sector data.

Is that clever or what? If you play the movie back in a 2D player, you get a left-eye-view of the movie. And from the file listings I gave above, if you add the sizes of the 00001.m2ts and 00002.m2ts files together, you get exactly the size of the virtual (ie. it isn’t really there) 00001.ssif file.  Likewise for 00003.m2ts, 00004.m2ts and 00003.ssif.

It makes sense too. Presumably some part of the left eye view is identical to the right much of the time, and the rest is quite similar, so the 3D extensions files would basically contain ‘difference’ information (and, of course, wouldn’t need to carry any audio or other data streams).