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View Full Version : Length Inconsistancy between DVD and Rip: Bug or Feature?


MasamuneXGP
21st May 2006, 20:25
Hello. I'm just getting into encoding, and I'm having a problem that I'm beginning to suspect is not a problem.

For some reason, the rips I am producing are always a few seconds longer than the actual DVD movie. This isn't a few seconds of blackness at the start or end of the film, it's an expansion of the whole film. Eg, it starts with the same video frames perfectly in sync, but ends with the one frame in the rip seconds after the same frame in the DVD. Okay, so framerate issue right? Wrong. It can't be a framerate issue because the audio is in sync. Which baffles me. How can they be different lengths but the audio still be in sync?

Anyway, if the audio is in sync, who cares? Well, putting aside the fact that a different length implies that I'm doing something wrong, I was hoping to have chapters imbedded in my final mkv file. The chapters output by Chapter-X-tractor match the DVD times perfect, but later chapters don't match their cooresponding frames in my rip because of the length discrepancy. I'd prefer to get a rip that's the same length as the DVD.

So, to head off everyone's questions, allow me to post exactly what I'm doing. I'll be using The Matrix Revolutions, however, let me stress that this problem manafests itself for every DVD I own, meaning I must be doing something wrong.

Step 1: Put the disk in the tray. Open the DVD with Media Player Classic. According to MPC, the movie is 02:09:08. This length is confirmed by Chapter-X-tractor, DVD Decrypter in IFO mode, and all other media players that play DVDs.

Step 2: Loaded DVD Decryptor in File Mode. VTS_01_0.IFO and VTS_01_1 through 7.VOB are selected. Click the Rip button. Note that I have also tried it in IFO mode, with no change. Here's a screenshot of my settings for File mode:
http://img441.imageshack.us/img441/1396/dvdsettings8hc.png

Step 3: Loaded the VOBs ripped by DVD Decryptor in DGIndex. "Force Film" is checked for Field Operation. "Correct Field Order" is checked in the Options menu, if that matters. Saved the .d2v file and a .avs file is created with only two lines: LoadPlugin for DGDecode.dll, and Mpeg2Source for the .avs file.

Step 4: Loaded the .avs file in VirtualDub. File > File Information shows the length of the file to be 02:09:15. Seeking in the file confirms that it's not just seven seconds of blackness, the film has somehow expanded. And yet, the audio is still perfectly in sync. No idea how that's even possible.

I have tried five different DVDs (The Matrix Revolutions, The Ring, Minority Report, Die Another Day, and ReBoot - Daemon Rising) and they all have the same problem, shorter movies seem to expand less. This procedure is so simple that I'm beginning to think that this is normal. Maybe DVD framerates are screwed up like this or something? Worst comes to worst I could write a simple program to correct the chapter times, but if I'm doing something wrong, I'd like to correct it.

If no one sees any error in my method, I would really appreciate it if someone could try it themselves and see if their length matches perfectly so I can see if this is a fundamental flaw in DVDs in general or if there's definitely something wrong. Thanks, and sorry for my wordiness.

Guest
22nd May 2006, 00:49
Nice post -- very clear and concise.

I ripped Gladiator. Here's a key observation:

2:09.08 -> 7748 seconds
2:09.15 -> 7755 seconds

(30 / 29.97) * 7748 = 7755

DVDDecrypter while ripping is claiming that the frame rate is 30 fps! You can see it right there on the status screen. But why? IFOEdit also shows 30fps. But the rate has to be 29.97 for NTSC. Could it be something to do with "drop frame"? If so, and I suspect that is the reason, this becomes an authoring issue and we might have to move it to DVD Authoring. :)

Google for "DVD drop frame".

I will ping mpucoder about this. jdobbs may know something about it as well.

mpucoder
22nd May 2006, 02:05
Yes, it's a drop-frame / non-drop thing. DVD uses non-drop for all timecodes and elapsed times, but, of course, the video plays at 29.97 So 2997 frames will play for 100 seconds, but show as 99 seconds and 27 frames.
Put another way, 2:09:08:00 is 232440 frames, which will play at 29.97fps for 7755.75 seconds

MasamuneXGP
22nd May 2006, 02:41
Ah! So I'm *not* going crazy! Many thanks mpucoder. But I thought the proper framerate is 23.976 for films? In any case it shouldn't be too hard to write up something to multiply all the chapter times by whatever the multiplier is, now that I know it's not just a wrong setting. Actually, it would be nice if Chapter-X-tractor had an option to do that automatically. Hopefully it'll do that eventually.

mpucoder
22nd May 2006, 02:48
The chapter times need to be in non-drop form (the shorter time) for authoring programs.

Guest
22nd May 2006, 03:05
But I thought the proper framerate is 23.976 for films? Don't you know about 3:2 pulldown?