markyzno..I suspect the codec paks you installed may be causing a conflict.  MOV H264 definitely works in x3d.  I have tested various forms from files encoded with ADobe media encoder, soerenson, native dslr footage and camcorder files direct from card.  All played smoothly.  One of the things I have encountered with codecs and part of the reason i stopped installing codec paks is that programs sometimes get confused which version of conflicting codecs to use.  Sometimes they default to the one you want, sometimes to one that works but gives inferior results and sometimes they jus tstop working like what you seem to be encountering.  Not trying to diminish your results, but I suspect that is where your problem likely lays.

I for one am glad that they changed out the video engine defaults to using Microsoft’s Media Foundation framework. Now I can import mp4 videos. I could not do that before. I prefer that format over avi when I am working on a video for You Tube or Vimeo.
 
IMO Microsoft's Media Foundation is a much better engine then DirectShow. I will still use Sony Vegas, but this new engine will make it easier for me to master the audio for these tracks within Sonar. Hopefully it will be more reliable and glitch free. We will see.

mark..not sure if you want to go through the bother, but I would try first uninstalling all the codec paks and doing a fresh install of x3d.  If you have premiere you likely have all the codecs you will likely need other than high end specialty codecs you would need to purchase anyway.  One of the hazards of workarounds is that they tend to need rebuilding when the core element changes.

Well video seems to be importing/playing back fine for me in x3d, so I wonder if maybe it is a codec conflict for you Mark?
One issue I'm noticing though is that there is a black frame flash in the video window every time playback is started or stopped... is there any way to change this behavior? 
This will be really distracting and annoying when working on sound design where playback needs to be stopped and started quickly and frequently.

One of the first things I did was try video in Sonar X3d Pro. I have a camera that shoots in mov and is H264. It loaded find and played great. I should say it loaded rather quickly even though its a long movie. Thumbnails showed nicely too. I have no complaints with Sonar and video. 
 
 

John, do you get a black frame flash when you stop/start the video?  Just trying to see if this is something specific to my system - thanks!

I'm not seeing any problems with import and playback, but people should probably do some tests with HD export in MP4 format. The OP's comments about a blotchy picture (regardless of bitrate) are true for me too. System is clean of third party codecs.

StepD I ran into that problem too.  SO far for me, the solution was to manually enter in a higher bitrate.  Oddly, I could not confrim whether botrate was accepted because when I hit the encode option button again it went back to default settings.  However, if I entered a higher bitrate ( I used 15000000) it exported a file that was not blotchy

StepD I ran into that problem too.  SO far for me, the solution was to manually enter in a higher bitrate.  Oddly, I could not confrim whether botrate was accepted because when I hit the encode option button again it went back to default settings.  However, if I entered a higher bitrate ( I used 15000000) it exported a file that was not blotchy

Any enhancements to other features? Suchs as...
 
* Ability to automatically recognize frame rate of imported video.
* Video jog feature on the toolbar.
* Ability to calculate tempos between video "hit points".