RE: [MSE] Ad Insertion (was: [MSE] Timestamp offset mechanism)

Hi Aaron,

 

Thanks for your comments. 

 

Your assumptions on my first comment are correct, I believe a frame
accurate pause and track switch would be very useful. This was what I
was going for on my follow-up email when I suggested using a
TextTrackCue to signal the switch:
http://lists.w3.org/Archives/Public/public-html-media/2012Jun/0109.html/
. Kevin S and Steven R mentioned on this point that you could get a
non-deterministic delay if you use this method, but I don't think this
is a problem as long as the content is paused frame-accurately. A viewer
won't notice a delay if the switch happens in less than 0.5s, but maybe
this non-deterministic delay is much bigger than this? If this is the
case, then as you stated this may be something for the HTML-WG to look
at?

 

To answer your question on seeking back to an advert, this should be
dictated through business rules. A Content Provider may wish to only
show adverts at a given point in the timeline once. If you skip back to
the ad-break point or before and press play again you won't see any
adverts at that ad-break point. It's also conceivable though that you're
always shown the same ad's at a given ad-break or that new ones are
acquired each time. 

On a side note: From personal experience I never really want to watch an
advert again, but if the content provider wished to do so they could
make references to viewed adverts available within their application.

 

With regards to the overlap rules, maybe I have misunderstood them. If
for example you have a segment that is placed on the time-line at t=100s
-> t=110s and you want insert a 10s ad at t=105s, how would you achieve
this? From my understanding of the rules the last 5 seconds of the
segment would be overwritten by the ad and you'd somehow have to acquire
those last 5 seconds of that segment again and add them to the timeline.

 

In conclusion it appears to me that we are not being as comprehensive in
covering as many use-cases as we could by adding the complexity of the
timestamp offset mechanism.

 

Regards

Duncan

 

From: Aaron Colwell [mailto:acolwell@google.com] 
Sent: 10 July 2012 19:15
To: Duncan Rowden
Cc: public-html-media@w3.org
Subject: [MSE] Ad Insertion (was: [MSE] Timestamp offset mechanism)

 

 

Hi Duncan,

 

Sorry for the huge delay in my response. I was solely focusing on the
object oriented API spec changes for a while. I'll be more responsive in
the future. :)

 

Comments inline...

On Mon, Jun 18, 2012 at 4:25 AM, Duncan Rowden <Duncan.Rowden@bbc.co.uk>
wrote:

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.

[acolwell] These seem like policy decisions best handled by the web
application instead of the browser itself. I don't quite understand how
the ad won't contaminate the media timeline since at a minimum it would
increase the duration of playback by the duration of the ad. I also
don't quite understand how seeking is supposed to work. What if I decide
I want to seek back into the ad after it has completed and the main
presentation has resumed? Are you saying this wouldn't be allowed or
could cause me to see a different ad? All this sounds to me like you
need a different feature than what I am proposing here. It sounds like
you want some sort of way 

to trigger a frame accurate track switch or pause.

	-          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.

[acolwell] The ad does not need to be appended at a segment boundary.
The standard overlap rules
<http://dvcs.w3.org/hg/html-media/raw-file/tip/media-source/media-source
.html#source-buffer-overlapping-segments>  would apply which should
allow one to place the ad anywhere in the timeline. Care would have to
be taken though if any end overlaps exist because they may cause a gap
in the timeline.

	 

	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?

 

[acolwell] I think your best option would be to propose a frame accurate
track switch feature to the HTML-WG since this doesn't sound like a
MediaSource specific feature. If you had this then you could simply use
two source buffers (1 for media and 1 for ad) for this use case and then
use the track switch feature to switch between the tracks associated
with these buffers. You'd still need the timestamp offset mechanism
though so you could place the ad in the proper location in the timeline,
but using 2 source buffers would allow you to avoid the ad clobbering
the main presentation media.

 

Aaron 

 

	 

	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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