[x264-devel] x264, VBV & two passes

[Mathieu Monnier]

Hi,

After looking at the source code, I'm a little confused about the 
capability of x264 to respect a VBV buffer in a two passes encoding. In 
a single pass encoding, VBV constraints are ensured thanks to a per line 
regulation, but that one is specifically disabled for two passes. Why ? 
Is it because the second pass ought to have information precise enough 
not to underflow the VBV buffer only with a per frame regulation ? If 
so, why is the warning "VBV underflow" disabled for two passes ?

In the end, it seems the VBV buffer for a two passes encoding is used to 
define loosely a max bitrate. Is it a correct assumption ?

Regards,

Mathieu

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