[DanT]

Well VBR work with "quality" the encoder use an algorithm to calculate on the fly how much bitrate it need to obtain a specific quality. You specified the quality you want and the more you want the bigger is the files.

let say a song is soft first then goes with a bang.

so the bitrate may look like

96kbps..96kbps..96kbps....128kbps..320kbps...292kb ps...etc.

An other song may be complex all the way so like

320kbps...290kbps...288kbps...309kbps...

That why VBR has all kind of different size and different bitrate.

Here the page on lame with some explanation on how they do it
LAME MP3 Encoder :: GPSYCHO - Variable Bit Rate

Since I have no background in psycoacoustic encoding I have no idea what they are talking about and how they choose the bitrate.

Basically you choose the quality and the calculate the bitrate on the fly for you and varied it as need.

 

[Dzjudz]

Quote:

Originally Posted by Flag /img/forum/go_quote.gif Interesting, if that is the case, then does that mean that every song encoded with VBR has the same file size? *edit* Never mind, I found two of the same song in my collection and both are VBR. But in theory doesn't allocating bitrate for certain parts means that the song needs x amount of bitrate at x time? Yet my obviously it is not the case.

No there is no predetermined size for a VBR encoded file.

It doesn't work like this: VBR is 5MB, we'll see what points in the song are less complicated and give those low bitrate and what points are complicated and give those high bitrate.

It works like this: we'll see what points in the song are less complicated and give those low bitrate and what points are complicated and give those high bitrate, and we end up with a size that this song needs.


Example (arbitrary and probably inaccurate, but it will paint a picture):
A 2 minute song has 1 minute of silence in it.

A CBR file will fill all of the time with the same predetermined bit rate, even when there is no sound. It ends up a large file.

A VBR file will use 0 bit rate in the silent parts, but appropriate bit rates for the music parts. It ends up considerably smaller than the CBR file.

 

[krmathis]

Disc rot anyone?
Where the files slowly loose bits as time goes by...

 

[Flag]

Quote:

Originally Posted by Dzjudz /img/forum/go_quote.gif No there is no predetermined size for a VBR encoded file. It doesn't work like this: VBR is 5MB, we'll see what points in the song are less complicated and give those low bitrate and what points are complicated and give those high bitrate. It works like this: we'll see what points in the song are less complicated and give those low bitrate and what points are complicated and give those high bitrate, and we end up with a size that this song needs. Example (arbitrary and probably inaccurate, but it will paint a picture): A 2 minute song has 1 minute of silence in it. A CBR file will fill all of the time with the same predetermined bit rate, even when there is no sound. It ends up a large file. A VBR file will use 0 bit rate in the silent parts, but appropriate bit rates for the music parts. It ends up considerably smaller than the CBR file.

I understand what you're saying, but I think you misunderstood what I meant. I had two of the same songs, apparently, and both were VBR. They had different sizes and VBR, but the same amount of time. But if they are the same song, wouldn't that mean same ups and downs, equating to same bitrates?

 

[DanT]

Quote:

Originally Posted by Flag /img/forum/go_quote.gif I understand what you're saying, but I think you misunderstood what I meant. I had two of the same songs, apparently, and both were VBR. They had different sizes and VBR, but the same amount of time. But if they are the same song, wouldn't that mean same ups and downs, equating to same bitrates?

If the same files are encoded with the same encoder with the same parameter then they should be the same size

However

Different encoder may use different parameter to decide what bitrate to assign to each part.

Also you can choose the quality of the VBR, for example Lame -V0 will be encoded at a higher bitrate than Lame -V5

Here a brief wiki about lame quality setting
LAME - Hydrogenaudio Knowledgebase

 

[Dzjudz]

Yes you can also encode in different quality VBR as DanT said.