Final Bitrate different from specified bitrate

[St Devious]

Using Ultrafast preset for encoding. Input bitrate is 6000 Kbps, while output is like 5750-5800.

Just wondering if this is due to one pass only encoding or some parameter not being specified due to ultrafast preset ?

[nm]

How many frames did you encode?

[St Devious]

How many frames did you encode?

3179 frames

[nm]

That could be too little to hit the target bitrate accurately with 1-pass ABR. You can try to adjust ratetol (http://mewiki.project357.com/wiki/X264_Settings#ratetol).

[kemuri-_9]

1pass abr is never guaranteed to hit the target bitrate even with the minimum ratetol of .01,
that's what the 2nd pass is for.