I just got myself a Vita and i'm trying to understand specifically what kinds of videos it can play. I tried copying a MP4 video file but apparently it's not compatible with the Vita.

Sorry if this is an uneducated question.

From the ultimate faq posted in us playstation blog:

Q: What video and audio formats will PS Vita support?

A: PS Vita supports a wide array of audio files, including: MP3 (MPEG-1/2 Audio Layer 3), MP4 (MPEG-4 AAC), and WAVE (Linear PCM). Video formats supported include: MPEG-4 Simple Profile (AAC) and H.264/MPEG-4 AVC High/Main/Baseline Profile (AAC). Image and photo formats supported include JPEG, TIFF, BMP, GIF, and PNG.

From: http://psvita-forum.com/topic/1254-which-video-file-types-will-the-vita-readplay/

This is from an older@Jedted said:

I just got myself a Vita and i'm trying to understand specifically what kinds of videos it can play.

You may want to reencode those videos, anyways. There's no point in playing a 720p video at 1280x720 on the vita when its 960x500something. Even though the video you're dumping on the Vita may be an MP4, it may be encoded in a way that the Vita doesn't like.

Download Handbrake.

Take a quick peak in this thread:

http://www.giantbomb.com/playstation-vita/60-129/vita-profile-for-handbrake/35-537163/