[theora] Are two passes useful in CBR mode ?

Benjamin M. Schwartz bmschwar at fas.harvard.edu
Wed Mar 17 19:59:41 PDT 2010

thibaut bethune wrote:
> I try to use the video tag to post videos on my blog


> I've read that CBR is a better choice than VBR for web publishing
> regarding the way TCP/IP works.

Yes, but there is no such thing as CBR.  The equivalent of CBR in video is
buffer-constrained bitrate control, which makes sure that a user with only
K seconds of buffer will be able to play through the file while
downloading it at the target bitrate.

> I wander if the  --two-pass option in ffmeg2theora is useful or not,
> since the bitrate (and then the file size) is fixed. Can i expect a
> better quality or is it a waste of time in CBR ?

Two-pass is useful when you are doing "CBR".  It should improve the
overall quality of the result.  When doing VBR (i.e. constant-quality),
two-pass is not helpful.


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