IRC log of tt on 2016-07-07

Timestamps are in UTC.

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logging to
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RRSAgent, make logs public
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Zakim, this will be TTML
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Meeting: Timed Text Working Group Teleconference
13:59:51 [trackbot]
Date: 07 July 2016
14:00:22 [gadams_]
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14:01:33 [nigel]
Present: Harold, Pierre, Glenn, Nigel
14:01:38 [nigel]
Chair: Nigel
14:01:40 [nigel]
scribe: nigel
14:02:15 [tmichel]
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14:03:35 [mike]
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14:03:39 [nigel]
Present+ Mike, Thierry
14:04:32 [nigel]
Topic: This Meeting
14:05:27 [nigel]
nigel: We have stuff to discuss re TPAC, IANA registration and the BBC Safe Crop Area submission.
14:05:42 [nigel]
... Any other topics to cover, including AOB?
14:06:11 [nigel]
glenn: There's a new issue on TTML2 to discuss
14:06:24 [nigel]
group: No other business to discuss
14:06:30 [nigel]
Topic: TPAC 2016
14:06:51 [nigel]
tmichel: Every year at TPAC we need to fill the form for requesting material we need for
14:07:06 [nigel]
... the meeting. Every room is equipped with projector and power, the question is do
14:07:20 [nigel]
... we want more: having a Polycom speakerphone for remote joining by Webex,
14:07:23 [nigel]
... or a flipchart.
14:08:01 [nigel]
nigel: I think we normally ask for both. Does anyone on this call want to join remotely?
14:08:13 [nigel]
glenn: Given the possibility of travel issues it's a good idea to have it as a contingency.
14:08:21 [nigel]
tmichel: Ok I'll request both a Polycom speaker and a flipchart.
14:08:36 [nigel]
... Friendly reminder also: hotel reservations are open so if you plan to attend TPAC I
14:08:41 [nigel]
... invite you to make your hotel reservation.
14:09:41 [nigel]
pal: There's one hotel ~300m from the conference centre; the next one is significantly further away.
14:09:49 [nigel]
tmichel: The hotel is not very far from downtown I think.
14:10:10 [nigel]
14:10:33 [nigel]
... Accommodation:
14:15:52 [nigel]
Topic: Profiles Registry and IANA registration
14:17:37 [nigel]
nigel: I think we're waiting on info about the IANA review period prior to making updates to the document.
14:19:07 [nigel]
mike: We have no comments on the document. I'm not concerned about this and it's not
14:19:48 [nigel]
14:20:49 [nigel]
14:21:03 [nigel]
mike: It's a little concerning that there's no status as it suggests that W3C hasn't made the
14:21:12 [nigel]
... request to IANA yet. I'll send plh an email asking for a further update.
14:21:43 [nigel]
Topic: TTML
14:22:31 [nigel]
14:22:31 [trackbot]
action-474 -- Thierry Michel to Publish current github errata document for ttml1 to include dropntsc time expression semantic -- due 2016-07-07 -- OPEN
14:22:31 [trackbot]
14:23:33 [nigel]
tmichel: I think that's done...
14:23:40 [nigel]
nigel: This: doesn't seem to have it.
14:24:09 [nigel]
tmichel: I missed that, sorry, I will do that.
14:25:19 [nigel]
nigel: No other update on any of the actions in Tracker.
14:25:24 [glenn]
14:25:28 [nigel]
glenn: There's this new issue.
14:25:44 [glenn]
14:26:05 [nigel]
glenn: We had previously added an issue to deal with the use of offset time expressions
14:26:16 [nigel]
... in smpte timebase, which the SMPTE timing semantics in TTML1 Annex N.3 did not
14:26:37 [nigel]
... treat fully (or at all). Recently Netflix pointed out that there's a second type of
14:26:46 [nigel]
... expression that's not dealt with, which is the fractional seconds component of a
14:27:00 [nigel]
... clock time expression, which appears not to be prohibited in SMPTE mode, but is not
14:27:15 [nigel]
... dealt with in the annex or the formulas for counted frames. I need to tweak the
14:27:26 [nigel]
... formulas to address the potential presence of fractional seconds components.
14:27:41 [nigel]
pal: In SMPTE mode why would you ever use something other than a timecode expression?
14:27:52 [nigel]
glenn: That's a separate issue - I have no idea why you would want to, but the current
14:27:59 [nigel]
... syntax does not prohibit it.
14:28:08 [nigel]
pal: But do we want to permit that or encourage people to do that?
14:28:19 [nigel]
glenn: In the generic TTML language I don't see any reason to prohibit it because it is
14:28:29 [nigel]
... semantically interpretable in a reasonable fashion. I don't have an issue with a profile
14:28:42 [nigel]
... excluding it. That might argue that we should define a feature in TTML2 that does
14:28:50 [nigel]
... not require support for fractional seconds component.
14:29:04 [nigel]
pal: I'd go further and add a note that you should not do that unless we can think of a
14:29:05 [nigel]
... use.
14:29:20 [nigel]
glenn: Semantically I think it's clear what it would mean.
14:29:28 [nigel]
nigel: I have doubts about what it would mean.
14:30:15 [nigel]
pal: §6.2.11 says:
14:30:19 [nigel]
... "If the time base is designated as smpte, then a time expression denotes a [SMPTE 12M] time coordinate with which the content of a Document Instance is to be synchronized."
14:30:33 [nigel]
glenn: If you're using discontinuous markerMode then I would completely agree - in that
14:30:48 [nigel]
... case it does not have defined semantics. But in continuous mode it does have well
14:30:51 [nigel]
... defined semantics.
14:30:54 [nigel]
nigel: What are they?
14:31:07 [nigel]
glenn: In the formula called countedFrames, the variable called seconds would be determined
14:31:46 [nigel]
... from the seconds and the fractional seconds component.
14:32:02 [nigel]
nigel: I think that's strange - the fraction of seconds is indicated both by a decimal fraction and frames.
14:32:38 [nigel]
glenn: I agree that it's strange, but there is a well defined interpretation, which is to say
14:32:48 [nigel]
... that seconds is a real number as opposed to an integer number. It still comes out.
14:33:03 [tmichel]
Nigel; the action 474 was assigned to me during last week telecon on june 30th, but I was not attending this telecon. that explains why I wasn't aware of it ;-) will look into it.
14:33:10 [nigel]
pal: Regardless whether it is allowed and there's an interpretation of it, unless there's a
14:33:27 [nigel]
... reason to encourage it I would prefer not to. We should not use things in SMPTE timebase
14:33:34 [nigel]
... that do not look like SMPTE time expressions.
14:33:45 [nigel]
glenn: Right now in TTML1 it is permitted, so we cannot say it is not being used somewhere.
14:33:59 [nigel]
pal: My point is not that we can forbid it but that we can discourage it through a note.
14:34:13 [nigel]
glenn: Your comment would also have a reading on offset times in SMPTE continuous mode.
14:34:31 [nigel]
... Let's say we have a time like 5.4s - that would also have to be intepreted according
14:34:48 [nigel]
... the countedFrames formula. So we have to take account of this in countedFrames in any case.
14:34:56 [nigel]
... I view the tweak to cover both of these cases equally.
14:35:11 [nigel]
pal: But my point is that if someone uses this it seems prone to a mistake.
14:35:21 [nigel]
glenn: I have no problem adding a recommendation that raises that point, for example
14:35:35 [nigel]
... an informative statement that points out that SMPTE mode should be congruent to
14:35:50 [nigel]
... SMPTE12M expressions, which do not permit decimal fractions of seconds then it is
14:35:53 [nigel]
... not advised to use those.
14:36:02 [nigel]
pal: I think that would be good.
14:36:18 [nigel]
mike: There's another complication - SMPTE12M has been deprecated. Effectively SMPTE
14:36:33 [nigel]
... does not have a timecode representation other than the binary. It was always intended
14:36:46 [nigel]
... to be a marker only. There are all kinds of pitfalls!
14:37:01 [nigel]
glenn: I should also mention that I recall reading some SMPTE specs in the past regarding
14:37:12 [nigel]
... timecode where there was a fractional subcomponent of the binary timecode. I don't
14:37:21 [nigel]
... recall if it was ever used and what it was precisely.
14:37:35 [nigel]
mike: You could define a mapping to the binary 12-1. I think we went too far in
14:37:44 [nigel]
... engineering this because it wasn't intended to be anything more than a marker.
14:38:00 [nigel]
... There is a SMPTE spec that represented one manufacturer's way of representing timecode.
14:38:14 [nigel]
... You won't get to that specification from any of the references in TTML1.
14:38:25 [nigel]
glenn: Of course we did not reference the binary form and it has no direct exposure in
14:38:39 [nigel]
... TTML however conceptually there is a mapping certainly in discontinuous mode. Whatever
14:38:53 [nigel]
... the binary representation is it will have components to represent seconds, frames etc.
14:39:09 [nigel]
mike: There is a reference to 12M in TTML, and the only thing in there is the binary representation.
14:39:25 [nigel]
glenn: I use SMPTE12M as an adjective for the phrase "time coordinate". That wasn't
14:39:32 [nigel]
... intended to be a binary equivalent for example.
14:40:17 [nigel]
nigel: It would be reasonable to expect the fractions of seconds and frames, if both present, to be alternative rather than additives.
14:40:33 [nigel]
glenn: I would like it to be well defined, even if the definition is absurd, and I'd prefer to make it additive.
14:40:50 [nigel]
pal: In TTML1 all we can do is make a recommendation, but in TTML2 we should go further and deprecate it.
14:41:08 [nigel]
glenn: I would prefer not to make TTML1 documents non-compatible with TTML2.
14:41:14 [nigel]
pal: Deprecating is not obsoleting here.
14:41:33 [nigel]
glenn: Before I wrote this issue I reviewed the text in TTML1 §10.3.1
14:42:02 [nigel]
... Underneath this in the first paragraph it states "If a <timeExpression> is expressed in terms of a clock-time, then leading zeroes are used when expressing hours, minutes, seconds, and frames less than 10. Minutes are constrained to [0…59], while seconds (including any fractional part) are constrained to the closed interval [0,60], where the value 60 applies only to leap seconds."
14:42:18 [nigel]
... Originally before I reviewed this text I thought maybe we had some prohibition in place
14:42:29 [nigel]
... against using fractional components, but when I read this I realised that it actually
14:42:34 [nigel]
... includes the fractional part.
14:42:56 [nigel]
mike: I'm leaning towards this being unintentional because 12M has no concept of fractional seconds.
14:43:08 [nigel]
glenn: If we're talking about SMPTE continuous then we're bridging the semantics between
14:43:20 [nigel]
... 12M and media time. We're postulating a continuous time interval that doesn't apply
14:43:34 [nigel]
... in the true SMPTE discontinuous mode. We did that to be able to interpret durations
14:44:14 [nigel]
... and offsets that were not possible in the discontinuous mode.
14:44:39 [nigel]
pal: §6.2.6 note 2 advises: "Due to lack of industry consensus on the utility and interpretation of the continuous marker mode, authors are advised to avoid its use."
14:44:53 [nigel]
... The more we can do to simplify this the better.
14:45:10 [nigel]
glenn: For TTML2 we discussed deprecating it and our conclusion was not to deprecate it.
14:45:24 [nigel]
pal: Do you recall the reason for it?
14:45:28 [nigel]
glenn: I'd have to look that up.
14:45:41 [nigel]
pal: there's a note in TTML1 saying we are considering deprecating markerMode.
14:46:01 [nigel]
glenn: After TTML1SE was published we had a further discussion here that basically concluded we probably could not deprecate it.
14:46:17 [nigel]
... And that there were valid reasons for continuing to define it so that there is a mapping to media time.
14:46:34 [nigel]
... SMPTE timecodes are sometimes used not as labels.
14:46:59 [nigel]
mike: A clarification: when we're talking about deprecation do we mean smpte or markerMode?
14:47:05 [nigel]
nigel: markerMode.
14:48:00 [nigel]
glenn: In annex N it turned out to be mathematically useful to retain continuous for mapping dropMode to an unambiguous timeline.
14:48:16 [nigel]
mike: But that came about so we could map media times with frames to a continuous time.
14:48:36 [nigel]
... Hopefully we made it unambiguous and potentially useful but that does not mean that anyone is using it.
14:49:16 [nigel]
harold: As far I've seen we don't have any source document that has this issue. We noticed this when we were going through the spec.
14:49:37 [nigel]
pal: My suggestion is to deprecate but not prohibit.
14:51:44 [nigel]
nigel: I'm considering using SMPTE discontinuous right now for live subtitling in EBU-TT, where I need XXXX
14:52:06 [nigel]
glenn: One thing I haven't got around to is mapping discontinuous to continuous. I find many use cases where continuous is useful.
14:52:45 [nigel]
mike: SMPTE continuous - in what situation is that used?
14:53:18 [nigel]
nigel: For me, when there's some knowledge that the timecode for media is linear for some period.
14:54:23 [nigel]
mike: So it's media time with an offset?
14:54:25 [nigel]
glenn: Yes
14:54:36 [nigel]
mike: You could just use media time with hh:mm:ss:ff expressions.
14:55:26 [nigel]
glenn: You could certainly convert the labels to continuous times but there are complex situations where you have to effectively replay the media and run a clock alongside.
14:55:38 [nigel]
... Right now we don't have any mapping from labels to continuous time values in TTML.
14:55:47 [nigel]
mike: I don't understand why you want to solve that problem.
14:57:26 [nigel]
nigel: A use case is to issue a document for a live subtitle and have a dur to limit the end point. Then you have to use continuous to add the dur to the begin.
14:57:47 [nigel]
pal: Why not just use media time?
14:58:47 [nigel]
glenn: [scribe lost ability to recall due to being behind]
14:59:12 [nigel]
glenn: Even if we discourage use we still need a well defined meaning. There are other
14:59:26 [nigel]
... issues we have discussed, and we can spend more time discussing SMPTE continuous mode.
14:59:43 [nigel]
mike: I don't think there was ever any intention for the SMPTE timebase to permit both fractional seconds and frames.
15:00:23 [nigel]
glenn: The history was we started with SMIL 1 time expressions, and we introduced frames. It may be that when we did that we did not consider the repercussions fully.
15:00:57 [nigel]
mike: I understand. Or remove it. We need to think about this more. In the context of 12M (which we need to update because it has been deprecated) there is no concept of a mapping from seconds to frames.
15:01:12 [nigel]
mike: We could create one but the point is that if you start with 12M you would never have fractional seconds.
15:03:05 [nigel]
nigel: §10.3.1 does not permit fractions and frames together!
15:03:27 [nigel]
glenn: You're right. Now I have a better solution, for clock-time.
15:03:53 [nigel]
... Sorry I didn't notice that before.
15:04:11 [nigel]
nigel: Well that was a fun discussion anyway. Thanks everyone, we're out of time. [adjourns meeting]
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rrsagent, generate minutes
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I have made the request to generate nigel
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Regrets: Frans, Andreas
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s/XXXX/to be able to issue a document with a subtitle that begins at a particular time but that ends after a duration has elapsed if no other new data has arrived to replace it. To permit addition of begin and dur I need to use continuous mode.
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rrsagent, generate minutes
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I have made the request to generate nigel
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ScribeOptions: -final -noEmbedDiagnostics
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rrsagent, generate minutes
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I have made the request to generate nigel
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s/ anyway./.
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rrsagent, generate minutes
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I have made the request to generate nigel
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