[mythtv-users] Question about recording profiles - bit rate vs max bit rate

[Michael T. Dean]

On 05/10/2007 08:23 PM, Brian L. Walter wrote:
> Pardon the ignorance but I'm wondering what is the difference between 
> the bitrate you set for a transcoder,

average bitrate

>  and the max bitrate...

hard upper boundary

> and how do 
> the two interact?

generally by a bit of black magic it seems.  But, the encoders do a 
pretty good job of keeping the average bitrate relatively close to the 
value specified for reasonably-long videos (i.e. > 10 minutes or so).  
The max bitrate needs to be around 4/3 the average to allow headroom for 
fast-moving scenes and scene changes.  There's a point at which 
increasing the max bitrate will have no positive effects (and some may 
argue can create issues for the encoder), so more isn't necessarily better.

You can do tons of research to find "the right values" to use or just 
adjust them until it looks good to you.  After all, in the end, that's 
really what matters...  Note, also, that bitrate--and only 
bitrate--determines file size, so you're aiming for a good balance of 
quality and file size.

Mike