The Adobe Media Encoder is a fairly full-featured and widely accepted tool for that job and it will run in the background while you continue to work in After Effects or Premiere Pro.I would not recommend trying to output your AE Comp using H.264. If you intend on delivering your product to the public then it is extremely important that you use an app that is specifically designed to render to common delivery formats. I hope this clears a few things up for you. They are not intended for distribution to the public. A Mezzanine codec (or format) is a compression scheme widely accepted and adopted by many production companies and/or professional freelancers for use as digital intermediates and production masters because you can re-render them many many times without introducing any compression or color artifacts. The Output Module is very efficient at producing frame-based visually lossless digital intermediates and production masters using many of the standard Mezzanine codecs. Most of these new formats are not compatible with the frame based rendering that the Output Module uses so you'll have to use the Media Encoder for them too.

There are some new compression schemes that look like they may gain wide acceptance and deliver higher quality playback with lower demands on the CPU, but there are still compatibility issues. H.264 rendering in a Quicktime container is also no longer supported by Apple so that is why it was removed.

The Output Module (Render Cue) has never supported multipass rendering and unless it is redesigned from the ground up, it never will.

Compression and color artifacts almost completely disappear. H.264 also works best when you use multipass rendering. Right now it is the standard for multi-platform delivery and is supported on virtually all current devices that will play a movie (video). H.264 is a high-quality interframe MPEG compression scheme with a defined set of standards for frame size, frame rate, and audio format.

After effects h264