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benefits of constant bit rate versus variable?

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Jeff
benefits of constant bit rate versus variable?
by
on Nov 11, 2005 at 6:42:54 am

Don't do a lot of DVD burning, but which is better -- taste great or less filling?

What I mean is, is there an advantage to using variable bit rate rather than constant, or vice-versa? If so, why?

Thanks.


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daniel_l
Re: benefits of constant bit rate versus variable?
on Nov 11, 2005 at 11:37:45 am

Variable bit rate (VBR) encoding will generally give you higher quality for a smaller final file size. Usually takes much longer to encode than CBR as generall VBR requires 2 passes for the encode and CBR usually does this in one pass (although some tools allow 2 pass CBR)


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mhh
Re: benefits of constant bit rate versus variable?
by
on Nov 11, 2005 at 4:26:57 pm

If you only have a 10 - 15 min programme how does 2 pass make it better?
It will make it smaller, yes, but better??


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daniel_l
Re: benefits of constant bit rate versus variable?
on Nov 11, 2005 at 4:40:54 pm

You could say that a VBR encode with an average bitrate of 4Mbps and a peak of 8mbps will be equal in quality to a CBR encode of 8mbps. However the VBR file will be more efficient.
You could also say that if you did a VBR encode with an average bitrate of 2mbps and a peak of 4mbps that it will be of higher quality than a CBR encode at 3.9mbps.

Both VBR encodes will usually result in smaller file size.

CBR has the potential to waste bits
VBR makes a better use of bits

Apart from the datarate the only things that make it 'better' are the source and the encoding application and CODEC.



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Jeff
What kind of encoders do people here use?
by
on Nov 11, 2005 at 5:01:02 pm

This would seem to me to say that it's nearly always better to use VBR (unless you're in a hurry to encode or have a project where space isn't an issue).

I use Cleaner XL to encode stuff to mpeg 2. I know there's a range of encoding software and hardware out there. What kind do most people here use, just out of curiosity?


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Borjis
Re: What kind of encoders do people here use?
on Nov 11, 2005 at 5:12:13 pm


Tsunami is my encoder of choice.

Cinemacraft is also excellent.
A little faster too.

Procoder is arguably the best one of all.


All of them offer 1-Pass VBR btw.
It's quite common now and thats how the set top DVD recorders
achieve flexible recording mode, with realtime VBR.


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eric
Re: What kind of encoders do people here use?
by
on Nov 11, 2005 at 5:59:08 pm

I would say ALWAYS use CBR unless space is an issues. Low cost encoders tend to deliver bitrate spikes once and awhile that send your overall bitrate over the 9.8 limit.


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Jeff
question re: tsunami
by
on Nov 12, 2005 at 3:21:16 pm

Downloaded this program to try it out, put 4 1-hour segments into it to do. It did them, except it did them all as one big 4-hour mpeg, rather than 4 separate 1-hour mpegs. What did I do wrong? How can I put multiple segments into it and have them come out separate segments rather than together as one long one? Thanks.


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Dave Friend
Re: question re: tsunami
on Nov 12, 2005 at 9:52:05 pm

Jeff,

You need to set-up each movie as a seperate encode project and submit each project to the batch function.

Hope this helps.

Be sure to check out the Cinema Craft Encoder too. Personal opinion is it's the best available.

Dave


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Jeff
Re: question re: tsunami
by
on Nov 13, 2005 at 1:25:42 am

Thanks, Dave. What makes Cinema Craft best, in your opinion?


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Dave Friend
Re: question re: tsunami
on Nov 13, 2005 at 4:31:56 pm

Jeff,

My opinion is based on an encoder "shoot-out" I devised and conducted in-house. A short sequence was cut together from a variety of sources. It included scenes that can be problematic for mpeg encoders - shots with fast motion, slow zooms on highly detailed and moving subject matter, computer generated animations, text on a subtly gradated background, text keyed on video, and slow dissolves between scenes with opposing motion. The edit was exported as an uncompressed avi. All the videotape sources were captured uncompressed via SDI. All animations were rendered to uncompressed files from the application they were created with.

The sequence was run through every encoder I had or could lay my hands on. The encoding parameters used (bitrate, GOP size and structure) were identical for each encoder. They were, in no particular order:
Canopus ProCoder 2.0
TMPGEnc 3.0 XPress
MainConcept (as found in Adobe Encore)
Ulead (in DVD Workshop 2.0)
Ligo (as found in discrete edit 6.5)
Cinema Craft Basic (version 2.69.01.10)

It was also output to Digibeta and encoded through a Sonic Solutions SD-1000 real time encoding card


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Jeff
Re: question re: tsunami
by
on Nov 13, 2005 at 7:31:51 pm

By the way, Dave, on this answer you gave -- I downloaded the trial version of Tsunami and the batch function is grayed out, so I guess if I'm going to do batch work I need to buy the full version. Can't see how to get the batch thing working here.


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mhh
Re: benefits of constant bit rate versus variable?
by
on Nov 11, 2005 at 6:01:48 pm

VBR - Smaller file size yes
But is the picture quality any better.
A 10 min programme cbr at say a data rate of 7, and a vbr at any settings, will the vbr be a better picture.
For these small programmes size/efficiency is not an issue, just best pic quality


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Dave Friend
Re: benefits of constant bit rate versus variable?
on Nov 11, 2005 at 8:02:10 pm

[daniel_l] "You could say that a VBR encode with an average bitrate of 4Mbps and a peak of 8mbps will be equal in quality to a CBR encode of 8mbps."

I think that if you test this theory you will find that the CBR looks better.

[daniel_l] "the VBR file will be more efficient."

True, read any description of VBR encoding and it will say VBR is more efficient. However, it is important to understand what efficient means in this context. It means the use of fewer bits of data to reproduce an image. In other words, the image is more highly compressed. Efficiency is demonstrated by requiring less input for the same output. The term has no additional meaning in this context.

It is possible, depending on the image contents, a higher compression would not be noticeable, but it will not ever look better.

[daniel_l] "You could also say that if you did a VBR encode with an average bitrate of 2mbps and a peak of 4mbps that it will be of higher quality than a CBR encode at 3.9mbps."

You could say that, but it would not prove to be a correct statement. Try it using your favorite encoder and you will see.

[daniel_l] "Both VBR encodes will usually result in smaller file size."

True, which points directly to the reason for VBR encoding: Cramming more program length into the same number of bits. There is no other reason to use VBR. If the program will fit in the available space (e.g. on a DVD) at a given CBR encode, then there is usually no reason to employ VBR encoding.

Dave



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mhh
Re: benefits of constant bit rate versus variable?
by
on Nov 12, 2005 at 9:34:22 pm

At long last somebody else agrees, that if space is not an issue, cbr is probably better than vbr.
All frames getting the same compression, not some 3 some 5 some 7.
Plus half the compression time.
Thanks Dave


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Ron Shook
Re: benefits of constant bit rate versus variable?
on Nov 13, 2005 at 7:51:05 pm

Friendly Dave,

Hey, Ho! Nice thread. Liked your shoot out!

This entire thread has dealt with the value of CBR when space isn't an issue in terms of available DVD space.

Can you or anyone say whether CBR is also preferable because it has a contant bit rate and is less likely to choke a marginal player because the bit rate is all over the place with VBR, particularly a VBR where minimum and maximum rates are acres apart?

Ron Shook


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eric
Re: benefits of constant bit rate versus variable?
by
on Nov 14, 2005 at 12:31:23 am

" Can you or anyone say whether CBR is also preferable because it has a contant bit rate and is less likely to choke a marginal player because the bit rate is all over the place with VBR, particularly a VBR where minimum and maximum rates are acres apart? "

This is how I think..but many will argue it. My worry lies in the bitrate spikes that ALL encoders can produce putting you over the spec limit. You can put about 90 mins of MPEG on a DVD-5 with a CBR rate of 6mb/s. It just sound logical to me to provide a nice "clean" constant bit when its available.


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Dave Friend
Re: benefits of constant bit rate versus variable?
on Nov 14, 2005 at 2:32:23 pm

[Ron Shook] "Can you or anyone say whether CBR is also preferable because it has a contant bit rate and is less likely to choke a marginal player because the bit rate is all over the place with VBR, particularly a VBR where minimum and maximum rates are acres apart?"

Hi Ron,

I can not say with certainty. My gut feeling is that wide swings in bitrate should not cause any particular problem even for marginal players. The max rate of the file is readily available to the player and it should be setting up buffers accordingly.

I have not seen any more problems with VBR than with CBR in regards to playback skips and/or picture break-up. If the situation you wonder about was common then I would expect to see more problems with VBR than with CBR discs.

In either case I think playback problems are usually because of throughput issues - the player just can't pass the data fast enough. (Data Constipation?) It could be because the system can't process the data fast enough. But my feeling is that most of the time it is because the player has trouble reading the disc. That can happen at any bitrate but problems do seem to get worse as the bitrate increases.


Dave


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Ron Shook
Re: benefits of constant bit rate versus variable?
on Nov 14, 2005 at 11:14:44 pm

Dave & Eric,

Well, sounds like I should just use what I have to within commonly accepted practices and not worry further. Excellent!

Ron Shook


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daniel_l
Re: benefits of constant bit rate versus variable?
on Nov 15, 2005 at 9:47:55 am

Dave,

Just to clear up any misunderstandings, I was referring to a multi-pass VBR encode, not single pass, as I think you are.



DL


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Dave Friend
Re: benefits of constant bit rate versus variable?
on Nov 15, 2005 at 12:43:03 pm

[daniel_l] "I was referring to a multi-pass VBR encode, not single pass"

Hi Daniel. I was referring to multi-pass VBR.


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daniel_l
Re: benefits of constant bit rate versus variable?
on Nov 15, 2005 at 1:45:54 pm

With over 10 years being a professional encoder and 20 years as beta tester, author, consultant and trainer in the video industry , I have never delivered a high end job without using multi pass VBR.

To quote Ben Waggoner:
"No quality-concious encoder would ever put content on spinning disc without using 2-pass"

To Quote a Videosystems MPEG encoder shootout wtitten by Barry Braverman, a veteran DVD author and designer.

"......VBR encoding produces a much higher overall quality than CBR at the same target rate......"

http://videosystems.primediabusiness.com/ar/video_mpeg_encoder_shootout/#si...

Obviously your mileage varies.

DL



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mhh
Re: benefits of constant bit rate versus variable?
by
on Nov 15, 2005 at 5:28:08 pm

How does it do that then?


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mhh
Re: benefits of constant bit rate versus variable?
by
on Nov 15, 2005 at 5:38:35 pm

Sorry pressed the button to soon.

VBR will not assign a higher bit rate than set for difficult scenes, and apply a lower one for easy ones.
Overall less visual quality.
Great for getting lots on a disc.
But if all scenes (easy and hard) are encoded at say 7 mbs, then the overall image has to be better, or am I missing something?


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daniel_l
Re: benefits of constant bit rate versus variable?
on Nov 16, 2005 at 4:18:59 pm

"VBR will not assign a higher bit rate than set for difficult scenes, and apply a lower one for easy ones"

That's exactly what it's designed to do within the confines of your Min, Ave and Max settings

"Overall less visual quality"

Wrong.

"Great for getting lots on a disc"

Agreed, but not the only reason to use it.

"But if all scenes (easy and hard) are encoded at say 7 mbs, then the overall image has to be better, or am I missing something"

Yes you are: What happens one of those harder scenes requires, say for example, 8.0Mb/s?
A m-pass VBR encode would adjust the bit rate to cope with the extra complexity, the CBR encode would simply drop off in quality.


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daniel_l
Re: benefits of constant bit rate versus variable?
on Nov 16, 2005 at 3:50:06 pm

You chaps really should read this - especially from about page 38 - 43.

http://users.design.ucla.edu/~badgerow/dvd_primer.pdf

It may help a little with your understanding of the encoding process, but I'm guessing some of you will still quibble.






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eric
Re: benefits of constant bit rate versus variable?
by
on Nov 15, 2005 at 10:13:55 pm

With over 10 years being a professional encoder and 20 years as beta tester, author, consultant and trainer in the video industry , I have never delivered a high end job without using multi pass VBR.

To quote Ben Waggoner:
"No quality-concious encoder would ever put content on spinning disc without using 2-pass"

To Quote a Videosystems MPEG encoder shootout wtitten by Barry Braverman, a veteran DVD author and designer.

"......VBR encoding produces a much higher overall quality than CBR at the same target rate......"



I dont agree....especially when compatibility and file sizes is not the issue. Ive disscussed this with Barry and he aggrees it depends on what kind of encoder your using and your content. ive seen first hand what CBR can do to compatibilty efforts. even if a player is able to handle bitrate spikes(which most do fine)...it kills me to know Im sending out a disc to a client with them on thier.

Now "high end" is a different story...but most people here don't use high end encoders. If I were using an SD-2000 card..No i would use CBR because I wouldn't need it.


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eric
Re: benefits of constant bit rate versus variable?
by
on Nov 15, 2005 at 10:17:06 pm

Sorry :) - I ment to say " I would NOT use CBR because I wouldn't need it"


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daniel_l
Re: benefits of constant bit rate versus variable?
on Nov 16, 2005 at 4:08:27 pm

"Ive disscussed this with Barry and he aggrees it depends on what kind of encoder your using and your content."

Obviously. Nothing is more important than the content, and the (quality of your) encoder.

"ive seen first hand what CBR can do to compatibilty efforts"

I've seen first hand what multi pass VBR encodes can do for profit and repeat business, never having had a disc returned because of incompatibility.

"Now "high end" is a different story...but most people here don't use high end encoders."

By high end I meant important, relating to the content and the client.


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Ivan Zhuang
Re: benefits of constant bit rate versus variable?
on Mar 22, 2013 at 2:15:03 pm

Just found this thread - awesome!


A question about my month old Samsung 2012 plasma, PN60E6500.

What I do is copy an MKV movie file onto a USB thumb drive and directly insert that into the TV's USB port for video playback.

Most movies play flawlessly (that I've tested), however, I've had a couple of "problem" files.

Upon looking into this issue, I've sort of concluded it's a video encoding / compatibility issue with the couple movies that have failed during playback.

Are CBR video files generally more "difficult" to decode and playback properly than VBR encoded files?

The only "common" factors of the files that have failed to playback correctly "seem" to be encoded in x264/CBR/L4.1 - would this potentially present any problems?

Could this be an issue? Most movies have played back well, however, most movies also do not list video encode specs as specific as I listed just above.

Cheers guys!


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Amando Sanchez
Re: benefits of constant bit rate versus variable?
on Aug 17, 2017 at 10:47:35 pm

Ivan- to play the files you mentioned will require an MPEG4 player. Try VLC (https://www.videolan.org/vlc/index.html) and see if you could play your file using this player. /nD


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WTS(JManz)
Re: benefits of constant bit rate versus variable?
on Nov 16, 2005 at 4:41:31 pm

Not to be too argumentative, but I personally shy away from 'absolutisms'. There are, IMO, merits to using either CBR or VBR. When disc space is an issue, then I completely agree that VBR is the only way that one can produce reasonably high quality (visual) files using lower average bitrates. VBR's advantage is that the encoder is given a range to encode--using lower bitrates for less complex scenes (like talking heads) and bumping the bitrate up to cover more complex or high motion scenes. VBR still has to 'hover' around an average, and the encoder has to 'choose' when and where the bitrate should be adjusted. Unless you are a compressionist using a higher end soft/hardware encoder, you are probably not doing segment by segment encoding, and are leaving this task up to the encoder. All encoders are not created equal, and that's why one can detect differences (sometimes significant) between encoders given the same material. The lower the average VBR bitrate one chooses, the more the 'men are separated from the boys' when comparing encoders.

CBR does have it's advantages over VBR, especially with consumer and prosumer software encoders, when disc space is not an issue. This is a quote from Ben W on Canopus' forum for Procoder (excerpted from a similar 'raging' debate over VBR and CBR over two years ago):

"Yeah, a 8000 Kbps CBR file will always be at least as good as a VBR with a 8000 Kbps peak. The difficult parts will be at the same data rate, and the easier parts could be at a higher data rate than the VBR. VBR is only needed when disc space is the limiting factor instead of throughput."

A CBR file encoded at the maximum setting for VBR will always be as good, and most likely better, than the VBR counterpart. Using CBR eliminates the need for the encoder to make 'choices' about when and where to adjust the bitrate--a high bitrate is used throughout. Using a high CBR bitrate ensures that all complex scenes and high motion scenes are encoded with adequate bitrates--no worries about the encoder making poor choices. Unfortunately those scenes that don't need as high a bitrate (like squirrel hunting with an elephant gun--effective, but overkill) will also be encoded at a high bitrate, which in turn eats up disc space. This gets us back to where I started--if the content will fit on the media in question without concerns for this 'wastefulness', then CBR is a good option to consider. CBR encodes are generally much faster, which is an added bonus.

Your reference to the quote by Barry Braverman compares CBR files encoded at the same rate as the AVERAGE of a VBR encode--and of course his conclusions are accurate, but are irrelevant when one considers the above.

Jim


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mhh
Re: benefits of constant bit rate versus variable?
by
on Nov 17, 2005 at 8:45:56 am

Exactly

Unless a scene encoded at max 7 Mbps 2 pass VBR, is somehow encoded differently than the same scene 7 Mbps cbr.
The image quality is the same, if not slightly better.


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