Chapters start early?

Eigentor wrote on 8/2/2009, 12:15 PM
I've made a DVD (DVD Studio Architect 4.5) with a "Play all" button and then 10 buttons that play only chapters of that movie. They start (in) and stop (out) and go back to the main menu. My problem is that some of the chapters seem to start 2-3 frames early, but it does not show in the preview or the timeline, only after rendering and burning. I've played with the "In" to start it even later but without moving it too far, I still have the problem. I'm very green at all of this so I don't understand a lot of the terminology and I'm self teaching.

Comments

bStro wrote on 8/2/2009, 1:02 PM
It has to do with the way in which the video is compressed. DVDs use a file format called MPEG2, which was designed primarily to get (relatively) high quality content in a (relatively) small amount of space. It does this by cheating.

In a format such as DV AVI, the file stores every single frame in its entirety, one reason such files are so large. In an MPEG2, however, only approximately every 15th (in most cases, about two frames out of each second) is a complete image. For the other frames, the file stores only the difference between that frame and its neighbors. Then when the video is played back, the playback device (media player, DVD player, whatever) reconstructs each incomplete frame by looking at the complete ones and 'filling in" the additional data stored for the incomplete ones.

(I tried to avoid too much terminology. Google "mpeg2" to get the messy details.)

What all this is leading to is the fact that a chapter must start on a complete frame, and some of yours are probably on incomplete ones. Recent versions of DVD Architect (including DVDA Studio 4.5) warn you when you put a chapter marker on an incomplete frame. The marker flag will have a little exclamation point on it. Although it doesn't move the marker for you automatically, the chapter will (because it has to) be on a complete frame.

Rob
Former user wrote on 8/2/2009, 1:04 PM
This is caused by the i-frames of the mpeg. Chapter has to be on an i-frame, but you don't always know where you put the mark. DVDA will preview the way you mark it, but will render it on i-frames which can be up to 8 frames off.

If you use DVDA to make your chapter marks, after you place the chapter mark on the timeline, a little yellow exclamation mark will show up if it is not on an iframe. Left click on the chapter mark and start sliding it and ARROWS will appear which indicate where the iframes are.

HTH
Dave T2
Eigentor wrote on 8/2/2009, 1:21 PM
Ok, that makes sense, but I don't see the exclamation mark. Where does it appear, on the timeline? Also, is there something I can do in Movie studio when I render to a particular type of fromat that I can import to architect, to solve the issue of i-frames?
Former user wrote on 8/3/2009, 9:11 AM
The Studio version of DVDA may not have this feature.

Maybe someone else can fill in the blanks.

Dave T2
TOG62 wrote on 8/3/2009, 9:46 AM
I just checked and the Studio version does have this feature. In my display the chapter marks not on an iframe are yellow and the exclamation marks are very small. Those on an iframe are a pinkish colour.

Mike
Eigentor wrote on 8/3/2009, 3:16 PM
I've tried to replicate what you said, but all I get are yellow markers. I dragged the marker through 20 frames and remain yellow. And I don't see any arrows. I'll keep looking though.

So because I'm importing MPG2, I'm hamstrung by this i frame issue on starting my chapters.
If I import MPG would I also have this issue?
My chapters start with several identical frames (Text boxes); If I went back to VMS and edited each chapter to start with 8 identical frames, then in DVDA I could start my chapters on the last identical frame and I'd be assured to be starting in that chapter, not early, correct?
bStro wrote on 8/3/2009, 3:30 PM
FYI, chapter markers are orange, not yellow. If you're looking at something yellow, those are actually the In and Out points you're moving around. Those aren't really an issue here.

Here's a screencap of a DVD Architect Studio 4.5d timeline with three chapter markers. The 2nd and 3rd chapter markers are not on I-frames and show an exclamation point indicating so. (Note: the arrows indicating possible I-frames, not shown in this screencap, will be blue and will appear immediately above the video event.)



If you don't see similar exclamation points on the chapter markers in your project, than we may be barking up the wrong tree, and your problem lies elsewhere.

As for a solution, Vegas Pro has the option, when rendering an MPEG2 with markers already created in Vegas, to encode the file so that the I-Frames are created at those markers. I'm not sure if Vegas Movie Studio has this option.

Rob
Eigentor wrote on 8/4/2009, 2:22 PM
Great, thanks. VMS9b has an option to save markers to media file, I'm hoping that will do it. The pic was worth a thousand replys. I went ahead and created an AVI and an MPG2 in which I inserted each chapter start with 8 identical frames so that I should be able In on the last.

Can you tell me what "Quantize to frame" is?
bStro wrote on 8/4/2009, 2:52 PM
The Quantize To Frames option in Vegas ensures that, while you're editing, the cursor always moves along frame boundaries. For example, if your project has a framerate of 24 frames per second, the cursor will never move less than 1/24th seconds so long as Quantize To Frames is on. You should always leave this on when editing video. It is helpful, however, to turn this option off when editing audio since audio doesn't have "frames." The online Help has more information.

This is strictly an editing concern and is not related to the issue you're having with MPEG2 files and chapters.

Rob
rrrrob wrote on 8/6/2009, 9:17 PM
I had this same problem, but the cause in my case was much simpler: I did not have the timeline magnified enough for accurate chapter marker placement....once I increased the magnification, I could see that my markers were not exactly where I wanted them...