Why do chapter points take longer to load as DVD progresses?

Lastindependent · Post by **Lastindependent** » Sat Jul 15, 2006 11:31 am

Hi

I have a DVD with many chapter points. Selecting chapter pointers further down/through the DVD takes progressively longer to load.

It's as if for each chapter point, when selected, the player is going back to the start of the video and then scanning forward until it reaches the selected point.

Searching the net for something else a while back I found mild reference to varying ways to create chapters - frame indexing??

Anyway can anyone explain what is happening and offer any solution?

Regards

Kevin

DVDDoug · Post by **DVDDoug** » Sun Jul 16, 2006 11:08 pm

A bad/corrupt video file?

Whenever I've had trouble setting chapter points, it's been caused by a bad MPEG. Some of my projects were even crashing, and I got into the habit of saving frequently...

If your source files are MPEGs, this is the problem. Note that a bad MPEG will sometimes play-back OK, so it can be hard to tell. If you're using an edited MPEG, try an unedited one. (It was the editing that was corrupting my MPEGs.)

Another related symptom was DVDs with "lip-sync" problems. (See my tag-line/signature below?)

Lastindependent · Post by **Lastindependent** » Sun Jul 16, 2006 11:15 pm

Doug - not sure if you understand my question.

I've created the DVD (from AVI's) and I'm talking about a delay experienced when the DVD is being played on a set top box.

If you jump to the chapter points at the end of the disc they take longer to load than those at the start.

Devil · Post by **Devil** » Mon Jul 17, 2006 7:18 am

Isn't this logical, to some extent? Your menu is at the centre of the disc, your later points are towards the periphery. Does it not take time for the laser head to move across the few cm between them and find the exact position?

Lastindependent · Post by **Lastindependent** » Mon Jul 17, 2006 7:22 am

Well no it doesn't sound logical to me.

The file is indexed via an IFO file - any portion can be "seeked" to use computer parlence. There should be no movement of heads in a sequential manner unless actually reading.

Does anyone know any other sites where some "DVD Gurus" might hang out?

Devil · Post by **Devil** » Mon Jul 17, 2006 7:51 am

You haven't understood what I'm saying. The physical movement of the head from the centre to the outside cannot be instantaneous and it obviously takes longer the farther it has to go.

Lastindependent · Post by **Lastindependent** » Mon Jul 17, 2006 7:56 am

I have understood what you are saying - but don't agree with your analysis.

It's no different to the disc in your computer - the heads don't "walk" all the way through a disc to get where they need to get. They "Jump" to the destination - it's called "seeking".

All the chapter points in a Video file on a DVD are indexed and this is stored in the IFO file.

So unless someone can tell me that DVDs don't seek to chapter points they read all the file and then start playing when they get there, what you are suggesting doesn't make sense - but I agree that is what it feels like - as I said in the opening post.

Devil · Post by **Devil** » Mon Jul 17, 2006 8:44 am

You still haven't caught on to what I am saying. You are quite right with the way the thing works but the mechanics of a DVD are far different than that of a hard disk. The average seek time of a hard disk may be, say, 6 ms but it may take double from one extremity of the head arm to the other and half for a short distance. The difference in time is imperceptible to the human eye, but it is perceptible when writing or reading video. This is why it is recommended to defrag a video HDD to avoid causing the head arm to make many excursions when reading or writing. DVDs are mechanically very different with a linear, not radial, displacement and, having moved, it has to adjust its focus. This takes time, which may be more perceptible. Also, the disc doesn't turn at 7200 rpm, otherwise the disc would mechanically shatter. DVD-ROM drives, such as are used in set-top players, have seek times of ~45-250 ms, the latter being easily perceptible to the eye. This is a purely mechanical state of affairs.

Lastindependent · Post by **Lastindependent** » Mon Jul 17, 2006 8:49 am

Ok, then maybe that's all that's happening - but it takes 20+ seconds to seek to the last chapter and 2 seconds the first.

I was speaking to someone who authors with the Apple offering (whatever it's called) and they were saying they can do this without any noticable delay.

Devil · Post by **Devil** » Mon Jul 17, 2006 10:13 am

Sorry, 20 or even 2 seconds is wrong. I've never seen anything like that. A fraction of a second, yes. Have you tried it on a different player?

Lastindependent · Post by **Lastindependent** » Mon Jul 17, 2006 10:19 am

Yes, someone else tried it on theirs and said the same (unprompted) - I tried it on another and it seemed OK.

There's no delay when used on a PC - I'd just like to understand it.

Devil · Post by **Devil** » Mon Jul 17, 2006 10:59 am

See your other thread.