manual/include/understanding-playlists.html

<p>
  A <dfn>playlist</dfn> is a list of regions ordered in time. It defines
  which parts of which source files should be played and when.  Playlists
  are a fairly advanced topic, and can be safely ignored for many types
  of audio production. However, the use of playlists allows the audio
  engineer more flexibility for tasks like multiple takes of a single
  instrument, alternate edits of a given recording, parallel effects such
  as reverb or compression, and other tasks.
</p>
<p>
  Each audio <dfn>track</dfn> in Ardour is really just a mechanism for
  taking a playlist and generating the audio stream that it represents.
  As a result, editing a track really means modifying its playlist in
  some way. Since a playlist is a list of regions, most of the
  modifications involve manipulating regions: their position, length
  and so forth. This is covered in the chapter
  <a href="@@working-with-regions">Working With Regions</a>.<br>
  Here, we cover some of the things you can do with playlists as objects
  in their own right.
</p>

<h2>Tracks are not Playlists</h2>
<p>
  It is important to understand that a track <em>is not</em> a playlist.
  A track <em>has</em> a playlist. A track is a mechanism for generating
  the audio stream represented by the playlist and passing it through a
  signal processing pathway. At any point in time, a track has a single
  playlist associated with it. When the track is used to record, that
  playlist will have one or more new regions added to it. When the track
  is used for playback, the contents of the playlist will be heard.
  You can change the playlist associated with a track at (almost) any
  time, and even share playlists between tracks.
</p>
<p>
  If you have some experience of other
  <abbr title="Digital Audio Workstation">DAW</abbr>s, then you might
  have come across the term <dfn>"virtual track"</dfn>, normally defined as a track
  that isn't actually playing or doing anything, but can be
  mapped/assigned to a real track. This concept is functionally
  identical to Ardour's playlists. We just like to be little more
  clear about what is actually happening rather than mixing old and
  new terminology ("virtual" and "track"), which might be confusing.</p>

<h2>Playlists are Cheap</h2>
<p>
  One thing you should be clear about is that playlists are cheap. They
  don't cost anything in terms of CPU consumption, and they have very
  minimal efforts on memory use. Don't be afraid of generating new
  playlists whenever you want to. They are not equivalent to tracks,
  which require extra CPU time and significant memory space, or audio
  files, which use disk space, or plugins that require extra CPU time.
  If a playlist is not in use, it occupies a small amount of memory, and
  nothing more.
</p>