W3C home > Mailing lists > Public > public-html-media@w3.org > June 2012

RE: [MSE] Timestamp offset mechanism

From: Duncan Rowden <Duncan.Rowden@bbc.co.uk>
Date: Mon, 18 Jun 2012 12:25:49 +0100
Message-ID: <124049A7728972469B1F2B326E65B5883BC6BB@bbcxues48.national.core.bbc.co.uk>
To: Aaron Colwell <acolwell@google.com>, <public-html-media@w3.org>
Hi Aaron,

 

I agree that the use-cases you state are important and need to be
catered for, but I have some reservations about the suggested API's. 

 

-          Ideally, when inserting an advert, this won't contaminate the
main media item's timeline. The reasoning for this is that when ads are
inserted, a content provider may only wish these to be viewed once. So
when rewinding back through a given point either another ad can be
inserted or playback can occur without showing an ad.

-          The point at which ads need to be inserted may not
necessarily coincide with a segment boundary, which as I understand it
would be required using this proposal.

 

As an alternative suggestion, I'd recommend keeping the separate media
items on their own timeline and define a way to switch at particular
points between the items?

 

Regards

Duncan

 

From: Aaron Colwell [mailto:acolwell@google.com] 
Sent: 15 June 2012 23:41
To: public-html-media@w3.org
Subject: [MSE] Timestamp offset mechanism

 

Hi,

 

Bug 17004 <https://www.w3.org/Bugs/Public/show_bug.cgi?id=17004>
proposes a mechanism for adjusting timestamps inside media segments.
This enables seamlessly splicing content together that doesn't
originally exist on a common presentation timeline. Inserting
advertisements into content is the most straight forward use case. There
has been some useful discussion in the bug comments, but we haven't
decided on which method signature to use for specifying the timestamp
adjustments.

 

Here are the proposed signatures at this point:

 

void sourceTimestampMapping(in double presentationTimestamp, in double
segmentTimestamp)

 -- or -- 

void sourceTimestampOffset(in double timestampOffset)

 

sourceTimestampMapping() just provides a way to say, "I want this
timestamp in the segment to map to this presentation time."

sourceTimestampOffset() is basically just saying, "Add this offset to
any timestamp in the segment to get the desired presentation time."

 

Fundamentally they do the exact same thing, but I'm looking for input on
which option people feel more comfortable with.

 

Which do you prefer?

Are you ok with the semantics outlined in the bug description
<https://www.w3.org/Bugs/Public/show_bug.cgi?id=17004#c0> ?

 

Aaron

 


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Received on Monday, 18 June 2012 11:26:29 UTC

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