[foms] WebM Manifest

Steve Lhomme slhomme at matroska.org
Thu Mar 17 23:52:19 PDT 2011

On Fri, Mar 18, 2011 at 12:10 AM, Timothy B. Terriberry
<tterribe at xiph.org> wrote:
>> In the case you describe the only drawback is that playback is not as
>> perfect as it can theoretically be. But that's expected when using
>> adaptive streaming anyway.
> The comments I gave before were not meant to be an exhaustive list of
> shortcomings. You also need to either a) know enough about the streams
> in advance to know whether or not such a switch will be successful
> (i.e., if you can't find that information in the manifest, then you'll
> need a full keyframe index, exposed in Javascript, which you would
> otherwise not need), meaning higher startup costs, etc., or b) you can
> try to make such a switch without knowing that it will succeed, and
> frequently download a lot of extra data which must be thrown away when
> you fail. Either way you add a lot of implementation complexity to do
> it. I guess maybe that all still falls under "playback is not as perfect
> as it can theoretically be", but that continues all the way down to, "It
> doesn't play at all."

The manifest usually don't contain all the possible switch points
(range information) for each variant. That information is deduced from
the index that is loaded at startup (which in binary format will take
less space than XML/JSON anyway). I think that's how DASH works and
IMO it makes more sense that way.

Steve Lhomme
Matroska association Chairman

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