user1702: I almost never get stuck with things like this and kinda figure things out myself... but I'm at a complete loss here. 
I've used Handbrake, X-Media Recode, and lots of other encoders and they're great.. but they just don't have clearly defined options for maximum and minimum bitrate control in VBR. That, or I just can't find the options. Is there a GUI I could use for this? Or is it only possible through command-line in x264 core? I've only been able to work with constant bitrate so far and I REALLY need to use variable bitrate.
I found these extra options and I think they might be for variable bitrate.. but experimenting and encoding with that still produces a result with constant bitrate:
VBV buffer size, VBV maximum bitrate, VBV initial buffer and Bitrate variance.
Any help would be appreciated.

user-1: Power-Inside provided a clear answer but there's a bit more too it.
You have to specify the maximum bitrate for "video" specifically, to achieve that you have to use this:
ffmpeg -i myfile.avi -b:v 4000k -minrate:v 4000k -maxrate:v 4000k -bufsize 1835k out.m2v


user1704: From http://ffmpeg.org/ffmpeg.html , you can do this in CLI.. not sure about GUI.

‘-maxrate bitrate’
Set max video bitrate (in bit/s). Requires -bufsize to be set. 
‘-minrate bitrate’
Set min video bitrate (in bit/s). Most useful in setting up a CBR encode   

Eg: "ffmpeg -i myfile.avi -b:v 4000k -minrate 4000k -maxrate 4000k -bufsize 1835k out.m2v"



1702: <p>I almost never get stuck with things like this and kinda figure things out myself... but I'm at a complete loss here. </p>

<p>I've used Handbrake, X-Media Recode, and lots of other encoders and they're great.. but they just don't have clearly defined options for maximum and minimum bitrate control in VBR. That, or I just can't find the options. Is there a GUI I could use for this? Or is it only possible through command-line in x264 core? I've only been able to work with constant bitrate so far and I REALLY need to use variable bitrate.</p>

<p>I found these extra options and I think they might be for variable bitrate.. but experimenting and encoding with that still produces a result with constant bitrate:</p>

<p>VBV buffer size, VBV maximum bitrate, VBV initial buffer and Bitrate variance.</p>

<p>Any help would be appreciated.</p>
 -1: <p>Power-Inside provided a clear answer but there's a bit more too it.</p>

<p>You have to specify the maximum bitrate for "video" specifically, to achieve that you have to use this:</p>

<pre><code>ffmpeg -i myfile.avi -b:v 4000k -minrate:v 4000k -maxrate:v 4000k -bufsize 1835k out.m2v
</code></pre>
 1704: <p>From <a href="http://ffmpeg.org/ffmpeg.html" rel="nofollow">http://ffmpeg.org/ffmpeg.html</a> , you can do this in CLI.. not sure about GUI.</p>

<blockquote>
  <p><em><strong>‘-maxrate bitrate’</em></strong></p>
  
  <p>Set max video bitrate (in bit/s). Requires -bufsize to be set. </p>
  
  <p><em><strong>‘-minrate bitrate’</em></strong></p>
  
  <p>Set min video bitrate (in bit/s). Most useful in setting up a CBR encode   </p>
  
  <blockquote>
    <p>Eg: "<strong><em>ffmpeg -i myfile.avi -b:v 4000k -minrate 4000k -maxrate 4000k -bufsize 1835k out.m2v</em></strong>"</p>
  </blockquote>
</blockquote>
