Bitrate Questions

[satansraiser]

Hello this will be my second post on doom9 forums so I felt I should say thank you to the moderators and hi to everone else. Well on to my two questions:

My first question is when I use the prepare phase on No Direction Home Disc 1 using the latest DVD Rebuilder and CCE SP 2.7 it tells me that the DVD is going to have to be compressed 59.3% to fit on a DVD-5 and that the bitrate is going to be 5,346/2,503/4,240 Kbs. But after it has been encoded at 7 passes and rebuilt I look at the bitrate in bitrate viewer and it is no where near to what DVD Rebuilder told me it was going to be. I guess my question is why these programs cant give me a solid answer.

My second question pertains to question one. When I use the prepare phase on Groundhog Day using the latest DVD Rebuilder and CCE SP 2.7 it tells me that the DVD is going to have to be compressed 68.9% and that the bitrate is going to be 5,284/600/3,909 Kbs. My question is how can a DVD that has to be compressed more have a higher bitrate.

Any info will surely help and just to make a note I put the files through DVD Remake Pro.

[rahzel]

i don't know how bitrate viewer works, but each vob file or cell has different bitrates. the number DVD-RB spits out is the OVERALL bitrate.

some movies have higher bitrates to begin with, so even if there is a greater amount of compression, the bitrate can be higher.

[jdobbs]

1. In order to keep the bitrate distribution across the entire feature proportional to the original encode, each segment is encoded with a different bitrate. The resulting overall bitrate is set to that shown during prepare.

2. You can't look at the bitrate in M2V files because they are all encoded at a fixed frame rate of 23.976. The reason is complicated and related to the capability to recreate hybrid streams. So the bitrate you see in the M2V may be as much as 25% below the actual bitrate as stored on the disc after prepare.

3. Percentages mean nothing except to give you an idea of how much the disc is going to change. The original bitrates might be anywhere in the range of 0 to 9800 kbs depending upon what the original author decided. Keeping that in mind, consider this: 68% of 7000kbs is 4760... and 58% of 9000 if 5220.

It's easy to start overexamining these things.... you have to trust that DVD-RB knows what it's doing. The important thing is: "What size is the output?" -- if it creates a DVD-R that is 4.32GB, then it was the correct bitrate.

[Edit: Corrected percentage value in paragraph 2.]

[satansraiser]

Since my first question was answered flawlessly by Rahzel and Jdobbs, I guess while I'm at it I'll ask a couple more seeing as I am a noob to encoding:

I prefer not to disclose my source for movies but according to my source all encoded DVD's must have a minimum bitrate of 3000. How can it be possible to keep a minimum bitrate of 3000 when some DVD's start out with a lower bitrate to begin with.

When setting how many passes to give with CCE is there a rule of thumb for DVD's with lower bitrates. Example 24 Season 1 Disc 1 I gave 10 Passes because the DVD had to be compressed by 51.5%. I guess my question is was I excessive with passes when encoding 24 Season 1 Disc 1.

If anyone is wondering why I am confused to this topic it is because for the longest time I have only known percents in DVD Shrink 3.2.

Thanks in advance:D

[jdobbs]

Your source is incorrect. The minimum bitrate for a DVD is only set by the muxing requirements. It's much, much lower than 3000Kbs. Usually the audio alone is enough to meet that requirement. You will find that there are sections (for example black or "no-motion" screens) that will only need about 100Kbs and still keep an extremely low quantization level (meaning extremely high quality).

Each pass you do has exponentially less affect on the output quality. For most sources you should do 2 passes. For those that are very difficult, do 3 passes. While everyone has an opinion on this... even CCE used to document in their User Manual that anything over 4 passes showed no measurable improvement in picture quality.

IMHO multiple passes are more of a sales gimmick than any real improvement in an encoder. After you've completed a single pass you have collected all the information necessary to determine how you want to allocate bits. The second pass does it. Any additional passes would more-or-less only correct any deviations in accuracy that you may have encountered in the preceding pass. That's why you will find that most encoders only provide 2 passes (e.g. CCE Basic, HC, QuEnc, ProCoder)

[satansraiser]

Luckly enough my friend Tyler is here:

Though I myself know nothing of downloading my friend Tyler says that the scene standard (Warez Scene) states that any DVD that plays under 3.0 MB/s will be nuked on nforce.nl or vcdquality.org.

Could they be referring to the Quantization Level.

Note: the reason for my questions is I would like to get it exactly perfect so I can start doing DVD's in batch mode.
I assure they're my own.

[jdobbs]

That just shows that the "scene" is not populated by engineers. ;)

Bitrate means very little when not considered with a lot of factors. For example, a source with an average bitrate of 2500 that was encoded with a high-quality encoder like CCE, ProCoder, or HC would very likely have better quality than something encoded at 4000 using the reference MPEG encoder from the standards committee. It would definitely look a lot better than something created by a transcoder at a much higher bitrate.

A film that has low action levels through most of it requires very little bitrate.

Anyone who sets their standards based upon bitrate or percentages alone are very likely not knowledgable about video.

If you want to talk to experts -- Doom9 is the place to be.

[satansraiser]

Jdobbs you really know ur shit and you made a great program. I personally thank you and just hope I haven't asked too many questions in one day.

:thanks:

[jdobbs]

No problem. That's why I'm here.