MP4 (Mainconcept H264) encoding in Squeeze 8

Hi,

I am currently in the process of moving away from FLV to the MP4 format, using the Mainconcept H264 codec) and no matter what I do to the settings in Squeeze the animated idents at the beginning of the videos look terrible - I am encoding at twice the bitrate used for our old FLV setting (so 1000kbps vs. 500kbps) and am using CABAC, an AVC profile 'Main', plenty of keyframes, and using i-frames and b-frames.

The videos are for use online as progressive download and are encoded to a size of 576 x 324 (a strange size I now but I was asked to create videos in the largest possible dimensions that our websites can support).

The videos themselves look perfect (much better than FLV) but the animations at the start are full of artifacts and heavily pixelated. This occurs whether I use a preset provided by Sorenson or create one of my own.

Has anybody else had this problem, or does anybody have any suggestions?

Just to clarify I'm using Adobe Premiere CS5 Production Premium and Sorenson Squeeze 8 on a Windows 7 PC.

I'd be really grateful for your help - I've spent days encoding video files at multiple different settings and am getting very frustrated.!

Thanks in advance.