Bitrate problem with ntsc

[LosKyllos]

Hi, I am trying to backup a dvd, but i have a problem with the bitrate.

The movie is 3 hours long with 448kbps audio, and a menu around 200MB.

It is a NTSC disc.

DVD-RB is calculating the bitrate to be around 2000, but I would expect a bitrate around at least 2700.

Isn't that right?

I hope someone knows what the problem is..

With a PAL source, I have no problems at all..

[jdobbs]

It isn't a problem. DVD-RB is calculating it right.

In NTSC video there are three kinds of sources. FILM at 23.976fps that is telecined, Normal video at 29.97fps, and hybrid sources that switch between the two randomly. In order to ensure any of these is working correctly (especially hybrid sources) you have to encode at a common denominator frame rate. DVD-RB encodes all NTSC sources at 23.976. It then replaces the flags when it rebuilds so the framerate is reconverted back to it's original state. This process is the reason DVD-RB works on all sources while some other methods that use encoders fail or create stutter.

So at encode time you may see a lower bitrate -- because the bitrate is based upon framerate... in other words, 23976 frames at 23.976fps is 1000 seconds but is only .8 seconds at 29.97fps. The true bitrate as it will exist on the output DVD may be 25% higher than what it appears when it encodes.

People sometimes try to outguess decisions that are made by DVD-RB -- but that can only get you in trouble. A lot of effort has gone into how it works in order to ensure the output is correctly encoded. You have to trust that it knows what it is doing...

[Added] In addition you have to calculate the space used for menus, IFOs, NAVPACKs, and packetizing overhead.

[LosKyllos]

Then I will try and rebuild it :D

Thanks a lot :)

Is there a way to see what the bitrate is after the encode then?

[jdobbs]

You can run bitrate viewer on the VOB files. But the one true way to know whether the calculated bitrate is correct is by looking at the output size. If it is about 4.32GB or so -- then the calculated bitrate had to be right... anything more would have made it too big to fit.