Domain Streams Attributes in PGCEdit

[manono]

There's a thread over at Videohelp.com where I gave some advice which turned out to be wrong, but helped the guy to solve his problem anyway. I became curious about the information shown in the Streams Attributes screen and left a question for r0lZ near the bottom:

http://forum.videohelp.com/threads/338483-Aspect-ratio-problems-please-help

And if anyone else knows the answer, feel free to chime in.

[Sir Didymus]

IMHO, the reason of the fail derives from the procedure followed by phdutton.

What this person would like to do is to store on his server just a single mpeg file, extracted from the DVD, containing a given title of the disc. This operation is not simple at all. There are situations where this is simply unfeasible.

Once the DVD authoring is done, there are no proper ways of playing back a given DVD title other than by mean of a DVD player. I mean a player, sw or a standalone, which is specific for the DVD playback; the generic media players are improper - or unuseful - for that job because they may discard or bypass the info contained in the IFO files. In other terms, it is wrong, in principle, to extract just the VOBs or the MPEG2 streams from a DVD and to play these files by using some media player.

It is always necessary that the DVD palyback is compying with the DVD standard and that the process of playing the DVD titles is "controlled" by means of the information contained in the IFO files.

To understand what I mean, let think about a multistory DVD with interleaved cells: the individual cells of different stories are sequentially stored in the mpeg2 stream, so any attempt to play back the mpeg2 stream directly with a media player, will fail, if the playback is not controlled by using the information contained in the IFO files.

The proper procedure to use in the case reported would be to rip the disc in FULL mode. Then to eventually edit the disc by using whatever tool that keeps intact and consistent the DVD structure (like PgcEdit or DVD Remake, for instance). Then to play the DVD content or the individual titles by using a good (software) DVD player.

Cheers,
SD

[manono]

Thanks, Sir Didymus. What confused me was PGCEdit's Domain Streams Attributes saying the DVD was 16:9. That information comes from the IFOs, right, and not the VOBs? And we already know that the VOBs have been encoded as 16:9 (he posted a MediaInfo text file earlier in the thread). Yet, it's a 4:3 DVD and plays as such in a standalone DVD player and one software player (VLC). After he converted the VOBs to MPG and in the process changed the DAR to 4:3, then the MPG played correctly also. I believe in most cases it's OK to just play VOBs or VOBs converted to MPG. It's not all that often you have angles or interleaved cells.

All this assumes the guy knows what he's talking about and is giving the right information. That's often a big assumption, but in this case the fellow seems pretty knowledgeable.

[r0lZ]

Sorry, I haven't noticed the thread at VideoHelp. (I visit that forum usually only once per week or so.)

Theoretically, I agree with Sir Didymus. A movie simply extracted from a DVD has many chances to not play right without the IFOs. The multistory example is excellent. But when the movie has nothing special, such as a simple movie with no interleaved contiguous cells, no still times or VOBU tricks, and a single VOB (I mean VOB ID, not VOB file), it should play fine in any player.

It is right that the aspect ratio stored in the IFO has precedence over the AR of the VOB, but that's not always respected by cheap players. Anyway, if it is identical in both cases, that should not be the source of the problem.

Note that the AR of the VTST and VTSM domains are stored in two locations in the IFOs: there is one copy in the VTSI_MAT table of the current VTS, and another one in the VMG_VTS_ATRT table of the VMG. To extract the information, PgcEdit looks in the VTSI_MAT table, and ignore the VMG_VTS_ATRT table. Of course, it updates both tables when the information is modified by the user. Maybe the information is right in one table, and wrong in the other one (and in the VOBs). If it's the case, the display depends of the table used by the player. To verify that theory, it should be sufficient to open the Domain Stream Attributes GUI, OK it and save the DVD. If most players display the movie with a wrong AR, that means that the information in VTSI_MAT is wrong, and that it was right in VMG_VTS_ATRT.

[manono]

OK, thanks r0lZ. If I'm understanding you correctly, the playback DAR is stored in two places in the IFOs. He said the DVD played properly in both of his standalones as well as in VLC Player. And if it's really supposed to play as 4:3, then the real information is in a different place than the place where PGCEdit's Domain Streams Attributes gets its information. But maybe that's true only for this special and very unusual case, because the DAR is supposed to be the same in both places and only a few players get the information from the VMG_VTS_ATRT.

You also seem to be saying that changing the DAR to 4:3 in PGCEdit should be sufficient to have all the players, both standalone and software, play it as a DVD correctly. So, no players, even software players, get the information from the VOBs, but always from one of those two places in the IFOs?

Thanks again for the information. Maybe I should have suggested him changing the DAR to 4:3 in the Domain Streams Attributes which then should have then had all the players play the DVD correctly. But he still had to use DVD Patcher on the VOBs because he wanted an MPG file to play from his server.

[r0lZ]

Yes, *maybe* there were two different DAR settings in the IFOs, and in that case, the result is unpredictable.

Fixing the DAR in both places in the IFOs should be sufficient, that's right. But as I said, the precedence rule is not respected by some (rare) players, so it might be useful to fix also the DAR in the VOBs. Of course, if he wants to play the VOB files without the IFOs, or convert them, he must fix the VOBs anyway.

[Ghitulescu]

From what I know, all hardware DVD-players are required to consider the DAR only from the IFOs. Since a SW one must emulate a HW player, this should equally apply.
The situation become more complex as the DVD-player ceased to be simply DVD-players, but Multimedia-players.
I had a short look on the aforementioned thread, and, yes, looking in my collection, it seems that [some/most] BBC DVDs have this particularity, the IFOs mention 16:9 while the VOBs have their MPEG-2 part signalled as 4:3. Is this a form of copy protection or just the way their encoder works, I don't know.

[mpucoder]

Pan/scan encoded video actually should show a DAR of 4:3! The DAR applies to the display area, not the full picture. A pan/scan video should have a picture width of 720 and a display width of 540, with the DAR set to 4:3. BUT the ifo talks about the encoded picture DAR, with 4:3 LB or PS as display options. What appears sometimes that is incorrect is a pan/scan video with 16:9 DAR. Now, if there is no pan/scan involved the display area is the same as the picture area, and 16:9 is OK to use.
So where's the real culprit? A multimedia viewer showing a vob, which is, after all, an mpeg-2 program stream, should recognize that the DAR is for the display area, and if a sequence_display_extension is present re-compute the DAR for the full picture area. Since that is not always the case you can strip the sequence_display_extensions out and change the DAR to 16:9 for compatability with any player.