View Single Post
Old 26th January 2007, 18:57   #2  |  Link
r0lZ
PgcEdit daemon
 
r0lZ's Avatar
 
Join Date: Jul 2003
Posts: 7,469
A cell is made of little parts (called VOBUs, beginning with a Nav PacK and followed by some video, audio and subpic packs.)
A normal cell usually contains several VOBUs, unless it's a very short cell (such as a single frame.) Each VOBU has its own VOB/Cell ID combination.

An ILVed cell (interleaved cell) is a cell "mixed" with (at least) another ILVed cell. In the IfoEdit example above, cells 5 and 6 are interleaved together. This means that a VOBU of cell 5 is followed by a VOBU of cell 6, then again a VOBU of cell 5, then 6, etc...
When the cells are interleaved, only one ILVed cell is played at a time. For example, in this case, the player could play cells 2, 3, 4, 5, or 2, 3, 4, 6. The technique of interleaved cells makes it possible to play seamlessly cell 5 or 6 after cell 4, because the laser head has not a too long way to move to the VOBU of the cell it has to play. If cell 6 was located after cell 5, the playback would need to pause when it skips cell 5.

Interleaved cells are used in multi-angle Titles (such as in your example) where the cell to play is determined by the current angle (previously defined by a SetSTN command, or by the user if he changes the angle with the remote.) It is possible to switch easily and (almost) in real time the current angle, as the player has just to finish playing the current VOBU, and then switch to the next VOBU in the other cell. The multi-angle technique is often used to translate some parts of the original image with words in foreign languages. There are many multi-angle examples in Disney DVDs.

Interleaved cells are also used in multi-story Titles. In this case, only one of the interleaved cells is declared in the cells list of the PGC, and it is therefore not possible to change the angle during the playback, and there is no need to define the angle with SetSTN. Another, totally different Title is defined elsewhere in the same titleset, and in that PGC, the other interleaved cell is used. Another difference between multi-angle and multi-story titles is that, in the latter, the duration of the interleaved cells doesn't have to be exactly identical. Therefore, the multi-story technique is used in DVDs with several versions of the same film, with little differences in the story (such as happy or sad ending.) Hence the "multi-story" name. True multi-story titles are very rare, but the multi-story technique can also be used for complex technical reasons, like in Matrix 1, to disable the white rabbit BOVs when playing the regular Title, or enabling them when playing the film via the bonus menu. In this case, it's the subpic streams that are different in the interleaved cells, not the video stream.

Only very good or professional authoring programs and muxers are able to create multi-angle or multi-story PGCs, and the ILVed cells.
__________________
r0lZ
PgcEdit homepage (hosted by VideoHelp)
BD3D2MK3D A tool to convert 3D blu-rays to SBS, T&B or FS MKV

Last edited by r0lZ; 26th January 2007 at 19:07.
r0lZ is offline   Reply With Quote