FMLE Jitter on Mac

Question

I'm using a Mac tower, dual hex core, 16gb mem, a real beefy computer that's normally used for video editing.  I'm using this in conjunction with a Blackmagic Decklink Studio capture card, which is receiving 1080i 59.94fps video.
I have the following Flash Media Live Encoder (FMLE) settings:
H.264 Level 5.1, keyframe frequency 2 seconds
30fps Frame Rate (for output)
1920x1080 input size, with "maintain aspect ratio" checked
2 renditions, one at 2200kbps/1280x720 resolution, one at 600kbps/320x180kbps
Audio is in AAC format, stereo, 44.1khz, 128kbps bit rate
I'm streaming this to a Flash Media Server (FMS) on Akamai.
I keep getting a fair amount of jitter.  I've tried many many combinations and permutations of settings, but to no avail.  The settings listed are the settings that seem to minimize jitter most effectively for my setup.  Even so, when the output is viewed on Akamai, the video is jumpy, freezing frames for a fraction of a second, or seemingly skipping frames.  Even when I change the output video to 1920x1080 (because I've read that making the input/output the same resolution helps), I still get this slight jitter effect.
The output statistics are standard.  No drops, no buffer, constant frame rate output, everything looks to be operating properly.
Does anyone have any suggestions on what to try next?  I've also tried running FMLE from the command line on my Mac, but I keep having troubles with the FMS authentication, so I don't know if that would help or not.
I've tried contacting Adobe a few times now, but it seems that Adobe does not have a dedicated team to this product like its others, and getting support for this product over phone or chat has been surprisingly difficult.

Answer 1

Thanks for the reply.
I've used Windows machines before with no problems, but this studio that I'm working with wanted to start doing live streams, and only has Macs in the studio.  So naturally they want to take one of the $4000 machines they have for video editing, and also use it for live streams, as opposed to buying a new PC for live streaming.
As for playback, when I've used Windows machines for encoding with FMLE, I've had no problems with playback on Macs.  When encoding with a Mac, both PCs and Macs experience playback jitter.  Also if I use FMLE on a Mac to record an FLV directly to disk, the FLV will have some jitter as well, so it seems to be an issue on the encoding end, not the playback end.
I've not tried SD sources, because my clients would rather buy a new computer than go SD (client is making the HD aspect of the stream a big selling point in their marketing), but I have used less taxing configurations, such as only encoding a 320x180 600kbps stream, and still have seen some jitter.  But even with my CPU cruising at 11% for that 320x180 stream, it's having issues.
Another fun fact: my company had a license for Wirecast laying around, and I tried it out on this computer.  Same problems, actually to a greater degree.
Thanks for the link.  That's actually very similar to a PC encoder that my company just built, we just have a dual quad core to handle the HD encoding, but we're still waiting for it to come to us from the west coast.  We may end up carting it to and from the studio for their live streams, if we can't get this resolved.
Finally, Adobe has been having me do encoding tests for them, and has been running encoding tests of their own in the lab.  They say they've been able to reproduce the jitter problem on a Mac in their lab, and are working on a way to resolve the issue.  Here's hoping...