[FFmpeg-user] 2 pass encoding with hevc_nvenc

Peter White peter.white at posteo.net
Sun Sep 4 13:52:28 EEST 2016

04.09.2016 12:21, Carl Eugen Hoyos:
 > Hi!
 > 2016-09-04 10:56 GMT+02:00 Marco Diletti 
<m.diletti-at-yahoo.com at ffmpeg.org>:
 >> i am trying to encode with a variable bitrate, 2 pass encoding
 > How is this supposed to work (in a general sense, unrelated
 > to a codec or an implementation)?
 > Two-pass encoding indicates constant bitrate afaict.

No, it does not. If each frame got the same bitrate, which is the
definition of constant bitrate (CBR) in my book, 2-pass encoding would
be utter nonsense.
2-pass encoding is VBR with predictable bitrate.

 > Having a larger frame buffer for one-pass encoding for
 > better rate-control does make sense but that is not two-pass
 > encoding.

Correct, and two-pass encoding is like having the whole file as buffer,
since the codec analyses it in the 1st pass and makes the rate
decisions based on that analysis in the 2nd.


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