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

Re: [MSE] Timestamp offset mechanism

From: Mark Watson <watsonm@netflix.com>
Date: Wed, 11 Jul 2012 16:26:10 +0000
To: Aaron Colwell <acolwell@google.com>
CC: "public-html-media@w3.org" <public-html-media@w3.org>
Message-ID: <2EFD0848-7116-4021-A5C4-47107214AC94@netflix.com>
Actually, I liked the nextSegmentStartTime (option 3). That is, assuming I remember correctly that what it does: establish a mapping from internal media time to source buffer time such that the next segment is placed at the provided source buffer time. (strictly, the mapping is established when the next segment arrives).

This obviates the need for the app to understand much about the internal media time.


Sent from my iPhone

On Jul 10, 2012, at 11:50 AM, "Aaron Colwell" <acolwell@google.com<mailto:acolwell@google.com>> wrote:

Hi All,

I'm going to try to summarize what I've read on this thread to see if I understand everyone's position

1. Eric, Steve, & Kevin all support the sourceTimestampOffset() signature
2. Mark doesn't have a strong preference either way, but is leaning towards sourceTimestampMapping() because it is more explicit about the application needing to know about the internal timestamps in the media segments and how they should map to the presentation timeline.
3. The alternative nextSegmentStartTime()/clearTimestampOffset() suggestion mentioned at the bottom of http://lists.w3.org/Archives/Public/public-html-media/2012Jun/0095.html got no votes
4. Duncan feels this mechanism isn't sufficient to address ad-insertion use cases he cares about. I just started an Ad Insertion thread<http://lists.w3.org/Archives/Public/public-html-media/2012Jul/0033.html> to continue the discussion. This may require adding a new feature.

Let me know if this is correct or if I've missed something.


On Fri, Jun 15, 2012 at 3:40 PM, Aaron Colwell <acolwell@google.com<mailto:acolwell@google.com>> wrote:

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>?

Received on Wednesday, 11 July 2012 16:26:44 UTC

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