Introduction to Pro Tools : Pro Tools Concepts : Pro Tools Sessions : Media Files

Media Files
Pro Tools sessions create, import, export, and reference media files. Media files are audio, MIDI, and video files. Audio and video media files are stored separately from the Pro Tools session file. MIDI data is stored in the session file.
Audio Files
When you record audio into a Pro Tools session, audio files are created.
 
Audio files for each session are stored in a folder named “Audio Files.” Audio files are listed in the Pro Tools Clip List and can appear in an audio track. A section of an audio file can be defined as a clip. See Clip.
MIDI Files
When you record or enter MIDI into a Pro Tools session, all MIDI data is stored in the Pro Tools session file. You can import and export MIDI files to and from Pro Tools sessions, but MIDI recorded or otherwise created in a Pro Tools session does not automatically create new MIDI files.
 
Video Files
When you record or import video into a Pro Tools session, all video data is stored as the corresponding video file type (such as QuickTime). Video files can be created in (or copied to) the Video Files folder in the session folder. However, in most cases, Pro Tools references video files that have been captured by another application, such as Avid Media Composer®.