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ACTION-84: Summarize the info from Jean Pierre, and mail it to the group [SMPTE MXF editUnit Spec]

From: erik mannens <erik.mannens@ugent.be>
Date: Wed, 15 Jul 2009 12:38:49 +0200
To: <public-media-fragment@w3.org>
Message-ID: <00e101ca0538$70a8d260$51fa7720$@mannens@ugent.be>
Dear all,

 

 

Summarization of SMPTE 377M-2004 (MXF File Format spec) editUnit

 

Editable unit: The smallest portion of the essence container which can be
edited such as a field or frame.

 

Edit rate: A rational number that specifies the units used to specify the
duration of components in a track; the edit rate is the number of units that
equal one elapsed second. In a track which describes an essence container,
the edit rate is usually chosen to be the number of editable units per
second.

 

Edit unit: A period of time equal to 1/(edit rate), thus mostly 1/frameRate
or 1/sampleRate (which is the smallest time fraction per frame or sample,
e.g. 1.001/60 or 1/25 or 1/41000)

 

timestamp: editUnit * value (integer) = timepoint corresponding accurately
to one sample or frame within a media resource

 

 

An editUnit is usually a field for video, but could equally well be a frame
(comprising 2 interleaved fields, or perhaps a single progressive frame). An
editUnit for an audio-only application could be an audio frame. There's a
big resemblance to MPEG-7's mediaTimeUnit (e.g. mediaTimeUnit="PT1N25F"
which means "1 fraction" (1N) knowing that there are "25 fractions/s" (25F))

 

There are different approaches to representing the editUnit e.g. float or
fractional.

 

The editUnits are now also being used in all EBU metadata specifications and
it has also been adopted by IPTC for NewsML-G2.

 

Looking at the structure defined in our current MFWG draft, I don't know if
we want to simplify it by removing the references to different timecoding
schemes by just adding the editUnit.  In IPTC, for NewsML-G2, it was decided
to allow both as well as npt (with 3 digits after the "." for milliseconds).

 

 

Sincere greetings,

 

Erik Mannens

 

Project Manager

 

Gaston Crommenlaan 8 bus 201

B-9050 Ledeberg-Ghent, Belgium

 

T: +32 9 331 49 93

F: +32 9 331 48 96

M: +32 473 27 44 17

 

http://multimedialab.elis.ugent.be

 
Received on Wednesday, 15 July 2009 10:39:36 GMT

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