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benefits of constant bit rate versus variable?
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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……”
https://videosystems.primediabusiness.com/ar/video_mpeg_encoder_shootout/#sidebar
Obviously your mileage varies.
DL
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How does it do that then?
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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? -
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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Sorry 🙂 – I ment to say ” I would NOT use CBR because I wouldn’t need it”
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You chaps really should read this – especially from about page 38 – 43.
https://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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“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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“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. -
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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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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