I have been expermenting with the video on the 600d and have made a few discoveries that others may find helpful... Firstly I have been using the 70-300 lens and because I enjoy filming birds and wildlife have been using the 3x digi zoom. Some of this is obvious but I will post in case its of interest.
3x zoom works great but even going to 4x has a marked deterioration in quality. too much to be useful imho.
IS works great but if you use it, you will lose the audio due to noise (on the lens I am using anyway..
ISO 800 is 9/10 ISO 1600 is only useable if the light is forgiving..
because the zoom is soo huge not only is a tripod essential but getting to know it is also vital. You only have to breath and it shakes or moves the image. Not suprising I guess because the 300mm lens becomes 900mm or 1350mm (not sure which) . Either way even on a sturdy tripod its very sensitive.
Finally and most importantly , the link above is my attempt at making a little film with it. You may want to know that the wren shot is the only one at ISO 1600. f5.6
the goldcrest chicks at the end are all 300mm F8 3x zoom . very clear image I think..
Hope this is helpful to someone..
ADMINS, please don't think I'm pimping a link here , I,m far from bragging here just sharing my first foray into dslr video...