Chapter points drifting

dvdude wrote on 6/6/2004, 9:18 AM
I have a single MPEG with chapter points. Each point marks the start of the next act. Each previous act ends with fade to black, that's where each chapter point is set (they were set in Vegas prior to compression). The start of each act has a fade from black into a title which disolves into the actual video. I want a "play everything" and a scene selection on the main page. Taking the scene selection puts you into additional menus which will play only the selected act and return you to the menu you called it from.

This is the easy part. The problem is that although the entire project previews perfectly, when an individual act is selected, a few frames of the following title screen appear before returning to the menu. This only happens when the DVD is written but happens on at least two standalone players as well as WinDVD.

I tried rendering each act to a seperate MPG but I can't link them to perform the "play all"function. Any ideas why this is happening?

Comments

Electromen wrote on 6/6/2004, 9:33 AM
Try double clicking on the Scene. This should bring up the trimmer. It should show your chapter points, go to the end of the scene and set the end point back a few frames. "In point" and "End point" icons are rectangles with small yellow triangles in the upper corners.
dvdude wrote on 6/6/2004, 9:47 AM
Even at maximum magnification, the chapter pointx are set precisely where I need them to be (at the point of maximum blackness if you will....)

I tried moving them back a few frames, but then the remaining audio becomes a burst at the beginning of the next clip. I understand that MPEG-2 can't really be manipulated on a frame accurate basis, I'm wondering if there's any way to force a P frame generation at the markers when I compress.

Assuming, of course, that chapter points are limited to P frames.
thomaskay wrote on 6/6/2004, 10:06 AM
Please post any findings on your problem.
SonySDB wrote on 6/7/2004, 5:00 AM
DVDA's chapter points are only precise to 0.4 seconds. (Chapter points must fall on I-frames.)
dvdude wrote on 6/7/2004, 6:43 AM
Thanks for the response SonySDB. I'm at work now so I can't look this up but IIRC, the GOP structure is 18 frames (for DVD Architect compatible NTSC streams)? As I want the chapter points in the black level of a fade out/in sequence, would inserting an 18-frame black clip in the middle of each one then guarantee that each section would start and end in black level? Your 0.4 second figure would indicate that I could probably get away with 12 frames?

Sorry for the confusion, MPEG isn't really as well known to me as I would like but I did a little research and found that P doesn't stand for primary :o)
I (Intra) is what I actually meant.

TIA
SonySDB wrote on 6/7/2004, 7:12 AM
For an NTSC DVD, the maximum number of frames in a GOP is 18. If you're using 18 frames in a GOP, it is only precise to approx. 0.6 seconds.

To have each section start and end at black level, set 18 black frames between each section and set each chapter point to the first of the 18 black frames.
dvdude wrote on 6/7/2004, 7:14 AM
Got it! Just hope auto ripple helps me out in Vegas.

Info greatly appreciated.
Electromen wrote on 6/7/2004, 1:45 PM
would rendering and then importing in .avi format give more control instead of mpeg?
dvdude wrote on 6/7/2004, 2:22 PM
I doubt it - DVD ultimately requires compression into MPEG-2, it's the structure of the MPEG-2 file that gives this limitation it would seem.

It might be possible to have a switch in the encoder settings so that an I-Frame is always produced at a chapter point, but I don't know what that would do to the GOP structures' validity.
dvdude wrote on 6/9/2004, 7:44 AM
Ok - I inserted an 18-frame black clip after each marker point in Vegas (didn't go smoothly with the media generator, but that's OT - auto ripple DID work for me though) and recompressed.

In DVD-A, the video looks fine but the markers did not update, with the result that the chapter points are occurring progressively prematurely along the timeline. What's the best way to force these to refresh?

TIA
jetdv wrote on 6/9/2004, 7:55 AM
What if you move the markers to the MIDDLE of the 18 frame black area?
dvdude wrote on 6/9/2004, 8:11 AM
I guess it would snap forward to the next I-frame. I can't see in DVD-A where the 18-frame clip starts and ends, besides, I was very precise about setting them in Vegas. What I need is for DVD-A to refresh the markers from the media.

[EDIT] JET - Thinking about it a bit, moving the markers that way might put me back where I started - there is no guarantee that the next I-frame occurs inside the black clip if I were to do that. [/EDIT]
SonySDB wrote on 6/9/2004, 8:47 AM
You can refresh the markers from the media by...
1. In Project Overview window, double-click on the video
2. In the timeline window, click the "Load Markers" button (6th button from the left) on the toolbar above the timeline
jetdv wrote on 6/9/2004, 9:45 AM
SonySDB, when placing the chapter point, does it always go to the NEXT I-frame or does it go to the CLOSEST I-frame?
SonySDB wrote on 6/9/2004, 10:37 AM
Next.