[MEncoder-users] x264: vbv bufsize

[Loren Merritt]

On Thu, 6 Dec 2007, Nicolas Hesler wrote:

> What is the vbv bufsize exactly and how do I calculate what size it
> should be?
>
> Let's say for bitrate 3000 and vbv_maxrate 4500
>
> or
>
> bitrate 3000 and vbv_maxrate 9500

vbv bufsize is the amount of memory a constant bitrate decoder needs to 
allocate to buffering the incoming compressed bitstream. You don't 
calculate it. There are 4 possible cases:
* You want to target a specific hardware deocder, and its documentation 
says what bufsize it uses. Copy that size.
* You want to target a specific hardware deocder, and its documentation 
doesn't say what bufsize it uses. You're screwed.
* You want to stream to a generic software player. Any bufsize works, but 
the end user needs to specify the same (or larger) bufsize when playing. 
It's a tradeoff between quality and latency, and there are no rules for 
choosing an optimal value, any more than there are rules for choosing an 
optimal bitrate.
* You aren't streaming nor targetting a hardware decoder. Don't use 
constant bitrate.

--Loren Merritt