Clarify definition of epoch and epoch-related offsets #302
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spec/ttml1.xml
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| <div2 id="time-expression-semantics-clock"> | ||
| <head>Clock Time Base</head> | ||
| <p>When operating with the <code>clock</code> time base, the following semantics should be applied for interpreting time expressions, | ||
| as defined by <loc href="#timing-value-timeExpression"><timeExpression></loc>, and their relationship to media time and local real time.</p> | ||
| <p>The clock time base <phrase role="strong"><code>C</code></phrase> is related to local real time <phrase role="strong"><code>R</code></phrase> | ||
| expressed in an arbitrary (implementation defined) epoch <phrase role="strong"><code>E</code></phrase> | ||
| expressed in the applicable epoch <phrase role="strong"><code>E</code></phrase> |
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Reading this sentence alone, one wonders what "the applicable epoch" is. Why not say "expressed in the epoch defined by the Document Processing Context".
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That'd work, but the applicable epoch is now defined in the appendix text before the sub-sections begin, so I think it works as is.
spec/ttml1.xml
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| <div2 id="time-expression-semantics-clock"> | ||
| <head>Clock Time Base</head> | ||
| <p>When operating with the <code>clock</code> time base, the following semantics should be applied for interpreting time expressions, | ||
| as defined by <loc href="#timing-value-timeExpression"><timeExpression></loc>, and their relationship to media time and local real time.</p> | ||
| <p>The clock time base <phrase role="strong"><code>C</code></phrase> is related to local real time <phrase role="strong"><code>R</code></phrase> | ||
| expressed in an arbitrary (implementation defined) epoch <phrase role="strong"><code>E</code></phrase> | ||
| expressed in the applicable epoch <phrase role="strong"><code>E</code></phrase> |
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I would like to see the parenthetical "(implementation defined)" remain in some form.
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@skynavga Would the text suggested by @cconcolato address your comment since Document Processing Context is implementation-defined?
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@palemieux yes, that would work
spec/ttml1.xml
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| @@ -13406,7 +13405,7 @@ during playback, presentation timing is not affected. | |||
| <p>When operating with the <code>media</code> time base, the following semantics should be applied for interpreting time expressions, | |||
| as defined by <loc href="#timing-value-timeExpression"><timeExpression></loc>, and their relationship to media time and local real time.</p> | |||
| <p>The media time base <phrase role="strong"><code>M</code></phrase> is related to local real time <phrase role="strong"><code>R</code></phrase> | |||
| expressed in the applicable epoch <phrase role="strong"><code>E</code></phrase> as follows:</p> | |||
| expressed in the epoch <phrase role="strong"><code>E</code></phrase> (defined by the <emph>Document Processing Context</emph>) as follows:</p> | |||
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leave "applicable"; remove parenthesis; change to "as defined by ..."
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"as defined by" will be followed by "as follows", which I think reads funny.
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I thought you were going to use @cconcolato's text, which would be:
expressed in the epoch <phrase role="strong"><code>E</code></phrase> defined by the Document Processing Context as follows:
which is fine with me.
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I think you're both wrong but also right! The point is not to give the impression that the "as follows" explains how the document processing context defines the epoch. How about:
expressed in the applicable epoch E, where E is defined by the Document Processing Context, as follows:
note the use of a comma after Document Processing Context to separate the sub-clause.
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I added the parentheses to emphasize that "as follows" qualifies epoch E and not Document Processing Context
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I think proper parentheses are clearer here than commas. I'm still worried that the comma separated sub-clause could be misread.
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I have reviewed this issue and PR and conclude that no change is needed whatsoever. The original text qualifies epoch with "(implementation defined)", which means exactly what is intended. All of these efforts to point out that "(implementation defined)" means the same as "(document processing context defined)" serves no useful purpose and merely adds clutter to the document. |
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@skynavga Evidently other members feel differently. The question is whether you plan on formally objecting to the PR as currently presented. Recall that the text is purely informative. |
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I'm happy with the changes made after my review approval. |
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In the interest of moving forward, I am approving this change. However, I oppose this change and will not entertain it for TTML2. This change fails to take note that "implementation defined|dependent" is a term in use elsewhere in the document, and adds nothing that is not already stated.
Close #266