Video Losing Quality when imported to After Effects

Please provide more info, in particular:

What is the format, frame rate and resolution of your source footage?

What is the resolution and frame rate of your comp?

What are the output settings and format you use when you render?

Is the footage position in your comp something other than standard?  For example, in a 1920x1080 comp, a 1920x1080 footage layer with default anchor point should be positioned at 960, 540 with a scale of 100.  If any of these numbers are thrown out, particularly by decimal points, then every pixel of your footage will be rendered with some antialiasing, making it look a little softer.  Please select your footage layer, reveal all the Transform properties and post a screenshot.

There is no way to tell without knowing your workflow and render details. My guess is that you are seeing compression and or color artifacts or you didn't have the Render Que or Media Encoder properly set up. Unless you are pretty much an expert in video formats and compression, you should not be messing with the controls. Use the presets for everything from Comp size to rendering.

If you export the video, a quality loss can occure because you are encoding the video instead of copying. This is not an issue, but within how things are working. You can export the video to a higher class codec or higher bitrate to prevent quality loss as much as possible, still the video get's interpreted in some degrees.

To see why there is a quality loss in the preview, we need some screenshots.

*Martin