Overall bitrate issue/question

[Susana]

I've just encoded a DVD in Dual Layer Target Size (DVD9) mode.

- Reduction Level for DVD-9: 80,8%
- Overall Bitrate : 3.667Kbs
- Space for Video : 6.497.710KB
- Movie improvement from extra reduction = 16,6%
- HIGH/LOW/TYPICAL Bitrates: 5.987/379/3.667 Kbs

After this, I've demux video stream with PGCDemux to calculate real bitrate:

http://img133.imageshack.us/img133/830/snap1mm1.gif


Real bitrate is 4.003 kbps, very different from 3.667 kbps.

So what am I not taking into account ?

Thanks.

[SpazzHH]

Real bitrate is 4.003 kbps, very different from 3.667 kbps.

So what am I not taking into account ?

Thanks.

Perhaps the fact that that bitrate is the average for all segments on the disc, not just the main feature. Did you take that into account?

[Susana]

Ah, ok, thank you, I've always thought overall bitrate only refered to feature.

[jdobbs]

Usually the feature will have a higher bitrate than the extras -- also the values you are quoting are the ones before the extra reduction... so you can expect the feature to be at least 16.6% higher than it was before reduction.

[SpazzHH]

Usually the feature will have a higher bitrate than the features -- also the values you are quoting are the ones before the extra reduction... so you can expect the feature to be at least 16.6% higher than it was before reduction.

?

Regardless of how the bitrate is distributed, the average for all segments on the disc has to stay the same or the total size would change. No?

[jdobbs]

Right. The average bitrate will stay the same no matter how you spread it across the segments. With a finite number of frames and a finite amount of space -- the average is finite also.

What I was saying in my response is that more of the available space has been reallocated to the feature due to "steal space" -- and as a result its bitrate has increased by 16.6%. It also, very likely, had a higher average bitrate than the extras even before the "steal space" -- so it could have an average bitrate that is significantly higher than the 3667Kbs.

Instead of "before extra reduction" I probably should have said "before additional extra reduction".

[feedback]

Usually the feature will have a higher bitrate than the features --
I am confused.:confused:
Did you mean to say 'extras' in place of the second mention of 'features'?

Regards,

[jdobbs]

Yes, that's what I meant. It should have been made clearer in post #6... but apparently not. I could express myself much better if words didn't keep getting the way.