- From: Brendan Long <self@brendanlong.com>
- Date: Thu, 16 Jan 2014 14:57:46 -0700
- CC: public-html <public-html@w3.org>
- Message-ID: <52D855DA.6060803@brendanlong.com>
On 01/16/2014 02:08 PM, Aaron Colwell wrote:
> The file offset of the cue information in the souce file could be used
> to create the unique ID. Just using the start time, end time, and text
> would not necessarily be unique if there are duplicate cues in the file.
Using the file offset would probably work. I don't think this is
possible in GStreamer though. If this is possible in other relevant
media frameworks (FFMPEG, AV Foundation, Media Foundation), then maybe
it's something we should add to GStreamer.
> Does WebVTT or CEA-708 have rules to prevent 2 cues from having the
> exact same timestamps and text? Obviously such duplicate cues would be
> rare, but I'm just trying to understand if they are possible and
> making it clear what the UA behavior should be if they are allowed in
> the underlying formats.
WebVTT seems to allow cues which are exact duplicates:
>
> The WebVTT cue timings part of a WebVTT cue
> <http://dev.w3.org/html5/webvtt/#dfn-webvtt-cue> consists of the
> following components, in the given order:
>
> 1. A WebVTT timestamp
> <http://dev.w3.org/html5/webvtt/#dfn-webvtt-timestamp>
> representing the start time offset of the cue. The time
> represented by this WebVTT timestamp
> <http://dev.w3.org/html5/webvtt/#dfn-webvtt-timestamp> must be
> greater than*or equal to* the start time offsets of all previous
> cues in the file.[emphasis added]
>
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<div class="moz-cite-prefix">On 01/16/2014 02:08 PM, Aaron Colwell
wrote:</div>
<blockquote
cite="mid:CAA0c1bD+oPYC1f4J+T=8_DFc1R9C4OnN9y=vShrs=KHO29KR3Q@mail.gmail.com"
type="cite">
<div dir="ltr">
<div class="gmail_extra">The file offset of the cue information
in the souce file could be used to create the unique ID. Just
using the start time, end time, and text would not necessarily
be unique if there are duplicate cues in the file.</div>
</div>
</blockquote>
Using the file offset would probably work. I don't think this is
possible in GStreamer though. If this is possible in other relevant
media frameworks (FFMPEG, AV Foundation, Media Foundation), then
maybe it's something we should add to GStreamer.<br>
<br>
<blockquote
cite="mid:CAA0c1bD+oPYC1f4J+T=8_DFc1R9C4OnN9y=vShrs=KHO29KR3Q@mail.gmail.com"
type="cite">
<div dir="ltr">
<div class="gmail_extra">
<div class="gmail_quote">
<div>Does WebVTT or CEA-708 have rules to prevent 2 cues
from having the exact same timestamps and text? Obviously
such duplicate cues would be rare, but I'm just trying to
understand if they are possible and making it clear what
the UA behavior should be if they are allowed in the
underlying formats.</div>
</div>
</div>
</div>
</blockquote>
WebVTT seems to allow cues which are exact duplicates:<br>
<blockquote type="cite">
<p>The <dfn id="dfn-webvtt-cue-timings">WebVTT cue timings</dfn>
part of a <a
href="http://dev.w3.org/html5/webvtt/#dfn-webvtt-cue"
class="internalDFN">WebVTT cue</a> consists of the following
components, in the given order:</p>
<ol>
<li>A <a
href="http://dev.w3.org/html5/webvtt/#dfn-webvtt-timestamp"
class="internalDFN">WebVTT timestamp</a> representing the
start time offset of the cue. The time represented by this <a
href="http://dev.w3.org/html5/webvtt/#dfn-webvtt-timestamp"
class="internalDFN">WebVTT timestamp</a> must be greater
than<b> or equal to</b> the start time offsets of all previous
cues in the file.[emphasis added]<br>
</li>
</ol>
</blockquote>
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Received on Thursday, 16 January 2014 21:58:20 UTC