user1914: I'm new to After Effects, but my experience with video editing so far has been that audio and video are treated separately. When I add an mp4 to my composition, I get the video element, but I can't figure out where the audio is at. When I hit play on the preview toobar, the audio does not play. I checked to make sure "mute audio" wasn't enabled.
I'm sure it's something simple, I just need to be pointed in the right direction.

user10615: After Effects works differently than normal video editors.
To play audio on a composition (your video project), press 0 on the numeric keypad (or Ctrl+0) to start the RAM preview.
This way, After Effects loads the audio through the RAM. If you skip to parts of the video that are not in the green bar below your composition preview, you have to wait for AE to render it.

user1950: If you just play the comp it won't play audio. You need to do a RAM preview. Hit 0 (zero) on the numeric keypad or Ctrl+0 if you're on a laptop. 
. (period) on the numeric keypad (or for laptop ctrl+.) plays just the audio from wherever the playhead is.
If your footage does have audio, you will see the waveform in the preview thumbnail in the project window, and the item description will tell you the audio format, as below (in this case 44.1kHz, 16 bit unsigned pcm, stereo audio)

If the clip has audio and you bring it into a compositon you should see a little speaker icon on the layer with the audio, next to the eye icon, on the left.


1914: <p>I'm new to After Effects, but my experience with video editing so far has been that audio and video are treated separately. When I add an mp4 to my composition, I get the video element, but I can't figure out where the audio is at. When I hit play on the preview toobar, the audio does not play. I checked to make sure "mute audio" wasn't enabled.</p>

<p>I'm sure it's something simple, I just need to be pointed in the right direction.</p>
 10615: <p>After Effects works differently than normal video editors.
To play audio on a composition (your video project), press <kbd>0</kbd> on the numeric keypad (or <kbd>Ctrl</kbd>+<kbd>0</kbd>) to start the RAM preview.
This way, After Effects loads the audio through the RAM. If you skip to parts of the video that are not in the green bar below your composition preview, you have to wait for AE to render it.</p>
 1950: <p>If you just play the comp it won't play audio. You need to do a RAM preview. Hit <kbd>0</kbd> (zero) on the numeric keypad or <kbd>Ctrl</kbd>+<kbd>0</kbd> if you're on a laptop. </p>

<p><kbd>.</kbd> (period) on the numeric keypad (or for laptop <kbd>ctrl</kbd>+<kbd>.</kbd>) plays just the audio from wherever the playhead is.</p>

<p>If your footage does have audio, you will see the waveform in the preview thumbnail in the project window, and the item description will tell you the audio format, as below (in this case 44.1kHz, 16 bit unsigned pcm, stereo audio)</p>

<p><img src="https://i.stack.imgur.com/kVdoR.png" alt="AE project window showing clip with audio"></p>

<p>If the clip has audio and you bring it into a compositon you should see a little speaker icon on the layer with the audio, next to the eye icon, on the left.</p>

<p><img src="https://i.stack.imgur.com/tYbck.png" alt="speaker icon highlighted"></p>
