The best way to think of SR is that it widens the scanlines and distributes the picture information across them. Where you once had a scanline of 1 pixel thickness, after SR you have a 2 pixel thickness scanline. This itself reduces aliasing - but the aliasing can be reduced further by using an interpolation method designed to de-interlace or reduce aliasing - like EEDI (enhanced edge directed interpolation) and/or NNEDI and/or QTGMC (and/or possibly even SR again). EEDI widens your scanlines, except by keeping the exact information present in the original scanlines and interpolating the information for the new ones. Your 1-pixel scanline is now 4-pixels, and depending on what you've done the width is either doubled or quadrupled. You then resize down to your output resolution.