manual/include/transcoding-formats-amp-codecs.html
2017-02-13 22:03:38 +01:00

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<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 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 to back and use the original source of the video.
</p>