[xiph-rtp] Chaining

[Aaron Colwell]

On Tue, Aug 30, 2005 at 04:33:03PM -0400, David Barrett wrote:
> 
> Another motivation, however, is downsampling to a non-factor framerate.  
> For example, assume a 30fps camera -- you can only "regularly" broadcast 
> at 1, 3, 5, 15, and 30 fps.  But 15-30fps is a big range.  Assuming my 
> target is 22fps (such as picked by an adaptive rate adjuster based on 
> current conditons).  15 is unnecessarily slow, and 30 is too fast -- 
> both by significant margins.  Plus, switching from 15 to 30 instantly 
> (or worse, toggling back and forth if you're right on the border) is 
> jarring.  However, I can get an average framerate of 22fps through 
> irregular frame dropping.  It won't be as visually pleasing as a 
> "regular" framerate, but for some video (especially live video from 
> crappy webcams) it might be acceptable.

This is one of the reasons why I called out video as having slightly different
requirements than audio. If you use a 90kHz RTP timestamp sample rate you have
a lot more flexibility with the frame rates that you can use. Remember that
we are talking about timestamp sample rates not fps. If you take (1 / fps)
the numerator will be the timestamp delta between frames and the denominator
will be the RTP timestamp sample rate. If you use 90000 as the denominator,
you'll notice that there is a large fps range to play with.

Aaron

> 
> -david
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