How to export a .blend file to .MP4? I have a very slow school computer and the school year is wrapping up soon. I'm using the video editing part of blender, putting in my own music and videotaping for an English project. I rendered it with the default settings (because I don't know how to change them, started yesterday) and there's no sound. I went to go see what was wrong and opened my project back up, but the ability to edit the video or audio was completely blank. I just want my complete video rendered in .MP4 so my teacher can see it;; I'd like to save it so he can hear the audio as well, but when  I render it it saves as a .png and doesn't have sound.
You don't export a blend file to a different format.
You need to render the images or frames of the animation and encode them to a video format.

In the output settings select FFmpeg video as the file format.



there will be a new tab for Encoding options.



There you can select the container and the codec for the output file.

Container is the file format for the file, (Mov, Avi, Ogg, MP4, to name a few) sometimes is referred as a "wrapper".

Codec (short for Compression-Decompression) Is how the image is compressed. The picture quality, file size and processing power needed to view the file are largely determined by the kind of codec used and the settings used for it.

For 2.8

The interface is similar but it is further divided into Encoding and Video, but the same principles apply.



If you have already rendered the images as a .png image sequence. Then all you need to do is load those images into the VSE (video sequence editor), where you can also load the sound, then set the output to FFmpeg and the video container and codec of your choosing and render.