[x264-devel] rate control

[Dennis Munsie]

Hi --

I'm trying to figure out how to properly use rate control in x264 -- I am
encoding a stream where the frame rate changes periodically (it's a webcam
that drops the framerate while it's re-focusing).  How does x264 handle
applying rate control when it doesn't necessarily know how many frames it is
going to get over time?  When I set rc.i_bitrate, I do see the stream's
bitrate change, but it's always off by some amount -- i.e, I ask for
2500kbps and my stream will be 3500kbps.  If I ask for 500kbps, it will be
1000kbps.  It gets closer, but not quite there.  I assume this has to do
with not setting up the x264_param_t struct correctly, but I'm really not
sure what I need to set it up with.

I am using low-latency mode already -- is there anything specific I should
be setting?  b_vfr_input, i_fps_num/den and i_timebase_num/den look like
things I should be looking into, but I'm currently at a loss as to how to
set these correctly given my source stream.

Also -- do I need to set the i_dts for the picture to account for the
variable frame rate?  Currently I am simply starting at 0 and incrementing
by 1 for each picture -- I assume that I would need to set this differently
to let the encoder know that framerate is different now.

Thanks!

-- 
dennis
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