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RE: Issue 29 - SMPTE tests

From: Sean Hayes <Sean.Hayes@microsoft.com>
Date: Sun, 12 Apr 2009 14:20:17 +0100
To: "Glenn A. Adams" <gadams@xfsi.com>, Public TTWG List <public-tt@w3.org>
Message-ID: <AB3FC8E280628440B366A29DABB6B6E8046B7ECC3F@EA-EXMSG-C334.europe.corp.microsoft.com>
True. But what I meant was timebase="smpte" frameRate="30" smpteMode="NTSCDrop", sorry for the confusion. There is afaik no such thing as drop @ 30fps, so unless we mean 29.97 (in which case the frameRate setting is superfluous and confusing), then this has no meaning.

I'm generally in favor of generality, (and even being able to write things that have no meaning, as long as we are clear that this is the case). I'm no expert on SMPTE 12M, and I don't have the spec to check; but I'm not sure it is a continuous parameter space.

I will endeavour to find out what 12M actually allows.

Sean Hayes
Media Accessibility Strategist
Accessibility Business Unit

Office:  +44 118 909 5867,
Mobile: +44 7875 091385

From: Glenn A. Adams [mailto:gadams@xfsi.com]
Sent: 12 April 2009 8:43 AM
To: Sean Hayes; Public TTWG List
Subject: Re: Issue 29 - SMPTE tests

On 4/11/09 11:10 PM, "Sean Hayes" <Sean.Hayes@microsoft.com> wrote:

[SH] frameRate="30" smpteMode="NTSCDrop" - is this to be interpreted as 29.97 drop frame or an error?

[GA] I wouldn't interpret as an error, but rather as warranting reporing a warning (in a hypothetical 'dfxplint' program), for example:

WARNING: ttp:smpteMode parameter is ignored unless the value of ttp:timeBase is specified as "smpte"

The current text of Section 6.2.8 clearly states this:
If the time base, defined by 6.2.11 ttp:timeBase, is designated as smpte, then this parameter applies as follows: ...

Also, the current text of Section 6.2.11 states:
If the time base is designated as smpte, then ... In this case, the value of the ttp:markerMode and ttp:smpteMode parameters apply, as defined by 6.2.5 ttp:markerMode and 6.2.8 ttp:smpteMode, respectively.

[SH] With these tests, we can consider Issue 29 closed, however I'm wondering whether we ought to define that tickRate and tickRateMultiplier are only defined in clock mode="media", and that for clockmode="smpte" the smpteMode attribute only is defined, with the values :

[GA] I don't like enumerations of aggregrate parameter points in a multi-dimensional parameter space, at least for operational parameters, as there is always a corner case you haven't accounted for, plus it makes spec maintenance more difficult. However, I would not object to defining these as enumerated (and labeled) optional features in Appendix E, where each definition would specify the set of ttp parameter values for which support is required if the feature is supported.

[GA] Regarding the semantics of ttp:tickRate, it is presently defined as related to "media time" as follows:
The ttp:tickRate attribute is used to specify the tick rate of a related media object or the intrinsic tick rate of content of a document instance in case it is intended to function as an independent media object.

We don't discusss in the text whether the use of the 't' metric would be permitted when:

 *   ttp:timeBase="clock"
 *   ttp:timeBase="smpte"

It seems to me, that the tick metric is well defined for (1) timeBase="clock" and (2) timeBase="smpte" and markerMode="continuous". If there is no objection, then propose that we elaborate these two cases in the text.
Received on Sunday, 12 April 2009 13:18:13 UTC

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