So I have a project here,but the banding is horrible,I've tried to render out in 32 bpc ,but there is very small difference,also if i apply any noise to the footage the final size becomes very large.Any ideas?
Banding is caused by lack of color depth or large color blocks/limited number of colors due to compression. This could lie at a number of stages.
In your project. You are working (i.e. rendering fx and compositing layers together at too low a bit depth). Solution work at 16bpc (32 is a different beastie)
In your render. You are rendering at too low a bit depth. Most movie formats are 8 bit. It doesn't matter if your project is 16 bit, your output is 8 bit. Solution - render to a 16/32 bit image sequence, such as tiff16 or dpx.
Your screen is 8 bit. All LCD displays are 8 bit, so even if you're looking at a perfectly rendered 16bit file, you'll still see banding because your screen is 8bit. Solution - there isn't one.
My usual color depth workflow: I render my projects at 16bit into a 16 bit image sequence format, then at the end create a lightly dithered (grain added) movie file render to overcome banding artefacts.
I import the rendered 16 bit image sequence and the sound as a second stage, apply a Noise HLS (grain) layer. This should be just at the threshold of perception - that's enough for the dithering effect of the noise to break up the banding (experiment here - it all depends on the image / format / compression). You should try to stop short of obvious "fizzing" unless a noisy, grainy look is something you're trying to achieve. The heavier the compression you use, the more noise you will need to apply to cancel out the banding artefacts.
And yes, in compressed formats, noise will make the file bigger (it's more detail). In some cases, the file may be bigger than the uncompressed original.
Lossless compression in Ae using the Animation is such an example. Animation is visually-losslessly compressed with a kind of run length encoding (think of it a bit like a zip file: It's smaller, but what you get out is exactly what you put in) It groups together similar colored pixels that appear together in blocks. A black frame compressed with Animation codec disappears to almost nothing. But by adding grain, the pixels are no longer the same as one another and you will end up with a much bigger file.