VBR and Bitrate Calculators

[hech54]

I never understood the fascination of bitrate calculators. If the majority of video that people come across is VBR....what's the point?
Am I missing something here?
I have noticed that watching the final output size in MainConcept(for example) while adjusting the video bitrate is "pretty close" to what MainConcept predicts....but it's never dead-on accurate.
It's my understanding that VCD material was normally CBR that needed to fit onto a specific sized CD.....so what is the point of bitrate calculators these days?
Maybe it's because I normally deal with videos ~5 minutes in length, many from VHS sources, that I scratch my head at the fascination with bitrate calculators?

[Hikmet]

VBR is 2-pass encoding, and cannot calculated any program %100 accurate, because file size depend video and encoder.

If use Bitrate calculator, always choose file size small than 650 MB, example 620-630 MB for VCD.

[hech54]

VBR is 2-pass encoding, and cannot calculated any program %100 accurate, because file size depend video and encoder.

If use Bitrate calculator, always choose file size small than 650 MB, example 620-630 MB for VCD.

I don't want to know how to encode an archaic VCD....I'm asking what is the point of a bitrate calculator in this day and age, and I'm asking if they are not 100% accurate....why use them?

[Hikmet]

VBR is 2-pass encoding, and cannot calculated any program %100 accurate, because file size depend video and encoder.

If use Bitrate calculator, always choose file size small than 650 MB, example 620-630 MB for VCD.

I don't want to know how to encode an archaic VCD....I'm asking what is the point of a bitrate calculator in this day and age, and I'm asking if they are not 100% accurate....why use them?

Why? Because we need estimated values. Experience most important. Programs are only help us.

[Selur]

What I do:
1. I use 2pass encoding when I aim for a specific file size, 2pass encoding aims for a specific average bit rate. For calculation abr is normally good enough.
2. I use a bitrate calculator which calculates the average target bit rate in respect to:
a. the target size I want
b. the audio formats and bit rates I use
c. the video formats and bit rates I use
d. the container I use
e. attachments like subtitles when used
3. I run the bit rate calculator once before I start my 2pass 1st pass to see which average bit rate I can give the encoder for 1st pass, then I run the audio encoding and rerun the bit rate calculator and adjust the bit rates for video encoding. Now I start the video encoding and after the video encoding I do the multiplexing into the container I aim for.
This normally produces a file size which is nearly spot on around 1MB to small due to rounding errors and the nature of the calculation heuristics being heuristics. For m2ts the calculation if more off, which is due to the fact that I don't know a good formula to calculate the container overhead. (the formula I use fails for HD audio)
To be frank, I only do the first calculation and the rest is done by the GUI I use automatically.


So my answer to "what is the point of a bitrate calculator in this day and age, and I'm asking if they are not 100% accurate....why use them?"
Is that:
a. I use a bit rate calculator because I sometimes (not always) use 2pass encoding and aim for specific sizes (in example CD/DVD/USB stick size)
b. I don't need 100% accuracy, I'm happy if the final file size is 99%+ accurate (and always below the size I aim for)

Maybe it's because I normally deal with videos ~5 minutes in length, many from VHS sources, that I scratch my head at the fascination with bitrate calculators?

I normally deal with 2h+ files, for ~5min files I would probably not care much about bit rate calculators too.

Cu Selur

[jagabo]

Want to put a 127 minute movie on a DVD? You'll need to know what bitrate that will give you 4.3 GiB.

[hech54]

Want to put a 127 minute movie on a DVD? You'll need to know what bitrate that will give you 4.3 GiB.

Is CBR valid for DVD?

[jagabo]

Want to put a 127 minute movie on a DVD? You'll need to know what bitrate that will give you 4.3 GiB.

Is CBR valid for DVD?

Yes, CBR is valid for DVD. But CBR, vs. VBR doesn't matter. You need to know what bitrate to use. In the case of multipass VBR you set the average bitrate, the encoder works within the min/max restrictions and delivers that average. So you get a predictable file size. Some encoders are better than others at meeting that average.

[Cornucopia]

If you don't care about the filesize (when putting your clips onto gigantic capacity HDDs), and only care about the quality, don't use Bitrate-based encoding. PERIOD. Instead, use Quality-based encoding (CRF, etc).

But anybody who still outputs to either a specific bandwidth restriction (for streaming, or broadcast) or anybody who outputs for storage restrictions on CD/DVD/BD/USB/smartcard DOES often need to use Bitrate-based encoding (whether CBR, 1- or 2-pass VBR, etc).

BTW, VCD was designed using CBR encoding, because the CD medium was expected to be putting out a constant 1x bitrate during playback, and VCD needed everybit of quality that could be gotten out of the 1150kbps bitrate (it was still really too low, so why NOT make the average be the MAX?), and because MPEG1 encoders at the time (early-mid '90s) would have taken way too long to do a 2-pass VBR encoding.

Scott

Scott

[manono]

...so what is the point of bitrate calculators these days?

I make lots of DVDs and need to know the bitrate needed to fill a 4.37GB DVD5. Outside of that I use CQ-based encoding.