Has anyone else been confused by the Qmin setting? In ffmpegX it says: "Encode a VBR stream with the following quality loss (withing the limits of the specified bitrate) (Lower values mean better quality)"
So why shouldn't I always set it to 1? Of course I want the best quality within the specified bitrate...?! But strangely enough, my results weren't high quality at all, despite that I had set it to minimum quality loss...
So I went and checked the MJPEG Howto at: http://mjpeg.sourceforge.net/
and here is what it says: (short summary: don't use 1, choose 6 or higher for SVCD)

The -q option controls the minimum quantization of the output stream. Quantization controls the precision with which image information is encoded. The lower the value the better the image quality.

Usually you have to set up a maximum bitrate with the -b option. So the tricky task is to set a value for the -q option and the -b option that produces a nice movie without using to much bandwidth and not much artefacts.

A Quality factor should be chosen that way that the mplex output of Peak bit-rate and Average bit-rate differ for about 20-25%. If the the difference is very small < 10%, it is very likely that you have done something wrong. It is very likely the you have chosen the wrong values for the maximal bitrate or a to high quality factor.

A combination that will produce more artefacts you can count, is a SVCD with a maximal video bitrate of 2500kBit and a qualitfactor set to 1 or 2. For SVCD with a video limit of 2500kBit a quality factor of 7-11 fits quite good. If you use filter programs or have a very good source like digital TV, DVD like material or rendered pictures. If your SVCD/DVD player supports higher bitrates than the official 2788kBit/sec for the video and audio. Use the higher bitrate and a higher quality factor, action scenes for example will look much better.

The same (7-11) quality factor for a full size picture and a top bitrate of 3500 to 4000 kBit won't produce to much artefacts too.

For SVCD/DVD you can expect a result like the one described if the maximal bitrate is not set too low:

q <= 6 real sharp pictures, and good quality
q <= 8 good quality
q >= 10 average quality
q >= 11 not that good
q >= 13 here even still sequences might look blocky
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