60 lines
2.3 KiB
HTML
60 lines
2.3 KiB
HTML
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<p>
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This chapter provides a short primer on video files, formats and
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codecs – because it is often cause for confusion:
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</p>
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<p>
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A video file is a <dfn>container</dfn>. It usually contains one
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<dfn>video track</dfn> and one or more <dfn>audio tracks</dfn>.
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How these tracks are stored in the file is defined by the
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<dfn>file format</dfn>. Common formats are
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avi, mov, ogg, mkv, mpeg, mpeg-ts, mp4, flv, or vob.
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</p>
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<p>
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Each of the tracks by itself is encoded using a <abbr
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title="Coder-Decoder"><dfn>Codec</dfn></abbr>. Common video codecs
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are h264, mpeg2, mpeg4, theora, mjpeg, wmv3. Common audio codecs are
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mp2, mp3, dts, aac, wav/pcm.
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</p>
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<p>
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Not all codecs can be packed into a given format. For example the
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mpeg format is limited to mpeg2, mpeg4 and mp3 codecs (not entirely true).
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DVDs do have stringent limitations as well. The opposite would be .avi;
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pretty much every audio/video codec combination can be contained in an avi
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file-format.
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</p>
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<p>
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To make things worse, naming conventions for video codecs and formats are
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often identical (especially MPEG ones) which leads to confusion.
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All in all it is a very wide and deep field. Suffice there are different
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uses for different codecs and formats.
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</p>
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<h2>Ardour specific issues</h2>
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<p>
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Ardour supports a wide variety of video file formats codecs. More
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specifically, Ardour itself actually does not support any video at all
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but delegates handling of video files to <a
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href="http://ffmpeg.org/">ffmpeg</a>, which supports over 350 different
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video codecs and more than 250 file formats.
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</p>
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<p>
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When importing a video into Ardour, it will be <dfn>transcoded</dfn>
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(changed from one format and codec to another) to avi/mjpeg for internal
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use (this allows reliable seeking to frames at low CPU cost—the
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file size will increase, but hard disks are large and fast).
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</p>
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<p>
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The export dialog includes presets for common format and codec
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combinations (such as DVD, web-video,..). If in doubt use one of the
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presets.
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</p>
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<p>
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As a last note: every time a video is transcoded, the quality can only get
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worse. Hence for the final mastering/<abbr
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title="Multiplexing Audio and Video">muxing</abbr> process, one should
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always go back and use the original source of the video.
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</p>
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