problems with 3ivx and 'fast' settings

[rsvp]

I have been trying out the new 'fast' settings and find the speed is great. However, I have an avi which is a 3ivx and mp3 mux. I noticed on playing the avi with quicktime that the film is a little blocky around the edges of motion and this carries over to any encoding I do. VLC plays back the avi perfectly, so I disabled the 'encode with quicktime' option in the ffmpeg options tab. Encoding was rapid, but did not stop at 100% but continued onto 160% and rising with a huge file > 2.5 GB which was a little excessive for an SVCD! All I could glean from the info box was a lot of rc buffer underflow. I had the same result with fastVCD.
Am I right in thinking that if quicktime encoding is disabled then ffmpeg will be used instead? I am currently trying to encode a the movie as a vcd using mpeg2enc with the encode with mplayer option. The video appears free from 'blocks' so far so I 'll keep on with it and see if it produces a properly muxed vcd. Any ideas would be appreciated as I really would rather use ffmpeg to encode my videos.

[major]

I have an avi which is a 3ivx ... I noticed on playing the avi with quicktime that the film is a little blocky.

Have you installed the 3ivx codec from 3ivx.com?

so I disabled the 'encode with quicktime' option... Am I right in thinking that if quicktime encoding is disabled then ffmpeg will be used instead?

It is "decode with Quicktime", not encode. This defines which software is used to read the video from the input file (ffmpeg or Quicktime). After that step, ffmpeg is always used to encode.

[rsvp]

I installed the 3ivx D4 4.5.1 for OSx in my quicktime library folder and it appears that this is the root of the problem. I have removed it and put the XVIDDelegate component in its place. This has lousy framerate playback (about 12.5 frames per sec on my 800 eMAc), but does appear to do away with the blocky areas around the motion.
Any ideas about the problem when 'decode with quicktime' is unchecked?

[major]

Could you send me a link to download a small clip, so as I can test.

[rsvp]

Probably muppetry on my part, but how do I obtain a small clip from an avi. I tried copying from quicktime, but the resulting clip wouldn't open in VLC, so I have fudged something up along the way!

Oh, and the movie encoded with the XVIDDelegate componet, but it refuses to multiplex as mplex complains of dropping too many frames!