[Theora-dev] Black frames need higher bitrates than moving ones?!

Robert Huitl theora-dev at huitl.de
Sun Oct 3 06:56:30 PDT 2004

I'm capturing video from a webcam and encoding it using Theora through Zen's 
DirectShow filter.

I noticed that black frames (webcam lens shut) produce 45 KB/s (target bitrate 
is 400 kbps), while moving video is around 8-20 KB/s. How can that be? Is the 
encoder fooled by the background noise the webcam produces?
Maybe it has to do with the quality setting, though I don't know what it's for 
(there's already a bitrate setting) and what i.e. 30 means to it, but I could 
imagine that a quality calculation in the codec has problems with black 

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