E80 note: "image" copy markers NOT frame-accurate - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 3 Old 08-22-2003, 12:01 PM - Thread Starter
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Just discovered that when dubbing in high-speed mode (which preserves user-set markers), that going to DVD-R does not preserve the frame accuracy of their placement. It looks at if they're reset to the GOP headers, and thus can be off by as much as 15 frames (~500 mS).

Initially, I thought I must have done something wrong, since I never noticed this before. On the first burn, I did a couple segments, then removed the DVD-R and later put it back for the rest, before finalizing. Since I still had the content on the HDD, I re-did it, doing the full disc burn and finalize in one pass, without removing the disc. The results were the same.

I then tried bouncing material from the HDD to a DVD-RAM, and the markers were still frame accurate, as they remained going back to HDD. Evidently, when reformatting from VRO to VOB for the different disc formats, marker accuracy is sacrificed.

Just a word to the wise in case you're contemplating marking specific points on a program, for slide shows, etc. They're fine for normal segment marking, but to make sure that skips are clean (no brief flash from a preceding segment), you might want to step a bit into the next segment before laying down a marker.

- Tim
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post #2 of 3 Old 08-22-2003, 12:11 PM
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That's too bad. I've been spending for instance ~4 hours for a ~2 hour program making frame-accurate marks. I was hoping they'd remain intact when I dubbed to DVD-R later. Oh well.

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post #3 of 3 Old 08-22-2003, 03:11 PM
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It's a limitation of the DVD format, chapter points are on I-FRAMES only, not just any frame. And since an I-FRAME starts a GOP......

It's been that way forever in DVD authoring. The only way to get around it is to FORCE an I-FRAME when encoding, something 'image' copying obviously can't do.

It could (in theory) do an 'intelligent' re-encoding around the desired frame.. ie..

original  IbbpbbpbbpbbpbbpIbbpbbpbb
          ^     ^         ^
          |     | chapter |
          |---------------| I-Frame's

to this   IbbpbbIbbpbbpbbpbIbbpbbpbb
          ^     ^          ^
          |-----|----------| I-Frames's
so as to preserve the desired chapter points, but then it wouldn't be an image then, eh?

Obviously this is not true for DVD-RAM structures..

You know, I used to think it was awful that life was so unfair. Then I thought, wouldn't it be much worse if life were fair, and all the terrible things that happen to us come because we actually deserve them? So now I take great comfort in the general hostility and unfairness of the universe.
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