manual/include/copying-versus-linking.html

<p>
  <dfn>Copying</dfn> and <dfn>linking</dfn> are two different methods of 
  using existing audio files on your computer (or network file system) 
  within a session. They differ in one key aspect:
</p>

<h2>Copying</h2>
<p>
  An existing media file is copied to the session's audio folder, and 
  if necessary converted into the session's native format.<br />
  For audio files, you can control the choice of this format (eg. WAVE 
  or Broadcast WAVE). Audio files will also be converted to the session 
  sample rate if necessary (which can take several minutes for larger 
  files).
</p>
<p>
  MIDI files will already be in SMF format, and are simply copied into 
  the session's MIDI folder.
</p>

<h2>Linking</h2>
<p>
  A link to an existing media file somewhere on the disk is used as a the
  source for a region, but the data is <strong>not copied or modified</strong> 
  in any way.
</p>
<p class="warning">
  While linking is handy to conserve disk space, it means that your session
  is <dfn>no longer self-contained</dfn>. If the external file moves, it
  will become unavailable, and any changes to it from elsewhere will affect
  the session. A backup of the session directory will miss linked files.
</p>
<p>
  You can choose to copy or link files into your session with the 
  <kbd class="option">Copy file to session</kbd> option in the Import 
  dialog window.
</p>
<p>
  <img class="left" src="/images/225-ARDOUR_1_2_1.png" />
  &larr; This file will be imported in the audio/MIDI folder of your session.
</p>
<p>
  <img class="left" src="/images/226-ARDOUR_1_2_1.png" />
  &larr; This file won't be copied.
</p>
<p class="note">
  There is a global preference <kbd class="menu">Edit &gt; Preferences &gt; Misc &gt; 
  Session Management &gt; Always copy imported files</kbd>. If it is
  enabled, you will not be able to link a file.
</p>