[foms] WebM Manifest

Steve Lhomme slhomme at matroska.org
Thu Mar 17 14:32:08 PDT 2011

On Thu, Mar 17, 2011 at 10:24 PM, Mark Watson <watsonm at netflix.com> wrote:
> On Mar 17, 2011, at 2:10 PM, Steve Lhomme wrote:
>> That would avoid forcing the encoder the extra fragmentation
>> constraint and use the available bandwidth more wisely (better end
>> user quality).
> Not sure I understand the bit about quality: do you mean that by allowing the encoder to choose key frame positions you get better quality. Yes. But then you do have to take care to ensure the different rate encodes pick the same keyframe positions. Without modification they won't do that. What I've seen in the past is running the highest bitrate encode first, getting a trace of the keyframe positions and then feeding that into the other encodes. You need a modified encoder that supports that.

Yes, that's what I mean. Statistically I think there are good chances
the different variants/bitrates passed through the same encoder (and
same "GOP size") should produce the same keyframe positions with
little differences. Not having to synchronize the encoders would make
life of the encoder (and likely the rate control process) easier. And
on the playback side there's hardly any drawback. But that means
players have to handle the case they want to switch but the next
keyframe is not available in the variant it wants to switch to.

Steve Lhomme
Matroska association Chairman

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