I just discovered that after effects files can be rendered outside the program using media encoder. I had been rendering in after effects to .mov, then opening the file up in photoshop to render the .mov to an mp4. Not the quickest process but it worked. If I use media encoder to render my after effects comp would i still be able to work in after effects and edit and save the file being rendered in media encoder or is it locked? I also hear the media encoder is slower than the after effects encoder. What are the best practices for taking an after effects comp and making it an mp4 (h264)? Thanks...
Depending on what you're doing the AME may be slower than using the render cue but it is the only thing you should be using to render H.264 files.
When you send a comp to the AME a virtual copy is made of that composition that is the source for that render. You may keep working on the same comp and make further changes but if you want those changes to show up you will have to send that comp to the AME again after you have made the changes.
Almost without exception I work on shots not sequences, and definitely never movies in After Effects. My average comp is probably seven seconds, my average movie is probably 30 minutes so I use AE to work on effects shots that cannot be processed in my NLE. I almost always send a comp to the AME to render a h.264 or a suitable production master or both and then I keep working in AE because I can't afford the time to wait around for a render. On almost all this is the most efficient workflow.