manual/include/transcoding-formats-amp-codecs.html

<p>
  This chapter provides a short primer on video files, formats and
  codecs – because it is often cause for confusion:
</p>

<p>
  A video file is a <dfn>container</dfn>. It usually contains one
  <dfn>video track</dfn> and one or more <dfn>audio tracks</dfn>.
  How these tracks are stored in the file is defined by the
  <dfn>file format</dfn>. Common formats are
  avi, mov, ogg, mkv, mpeg, mpeg-ts, mp4, flv, or vob.
</p>
<p>
  Each of the tracks by itself is encoded using a <abbr
  title="Coder-Decoder"><dfn>Codec</dfn></abbr>. Common video codecs
  are h264, mpeg2, mpeg4, theora, mjpeg, wmv3. Common audio codecs are
  mp2, mp3, dts, aac, wav/pcm.
</p>
<p>
  Not all codecs can be packed into a given format. For example the
  mpeg format is limited to mpeg2, mpeg4 and mp3 codecs (not entirely true).
  DVDs do have stringent limitations as well. The opposite would be .avi;
  pretty much every audio/video codec combination can be contained in an avi
  file-format.
</p>
<p>
  To make things worse, naming conventions for video codecs and formats are
  often identical (especially MPEG ones) which leads to confusion.
  All in all it is a very wide and deep field. Suffice there are different
  uses for different codecs and formats.
</p>

<h2>Ardour specific issues</h2>
<p>
  Ardour supports a wide variety of video file formats codecs. More
  specifically, Ardour itself actually does not support any video at all
  but delegates handling of video files to <a
  href="http://ffmpeg.org/">ffmpeg</a>, which supports over 350 different
  video codecs and more than 250 file formats.
</p>
<p>
  When importing a video into Ardour, it will be <dfn>transcoded</dfn>
  (changed from one format and codec to another) to avi/mjpeg for internal
  use (this allows reliable seeking to frames at low CPU cost&mdash;the
  file size will increase, but hard disks are large and fast).
</p>
<p>
  The export dialog includes presets for common format and codec
  combinations (such as DVD, web-video,..). If in doubt use one of the
  presets.
</p>
<p>
  As a last note: every time a video is transcoded, the quality can only get
  worse. Hence for the final mastering/<abbr
  title="Multiplexing Audio and Video">muxing</abbr> process, one should
  always go back and use the original source of the video.
</p>