[x264-devel] default level

[Loïc Le Loarer]

Le mardi 15 juillet 2008 à 19:51:13 +0200, Mathieu Monnier a écrit:
> > Why would you say that?  16 refs is decodable for SD at 4.1, 
> 
> But preferred level for SD is 3.0, which allows for 5 frames, and that's 
> roughly what apple tv does, if I'm not mistaken,
> 
> > and for HD resolutions at 5.1.  
> 
> Loic did point out that nothing hardware decodes 5.1.

I mean that nothing hardware decodes 5.1 fully, and this is also true
for software decoders (have you seen something able to decode 4Kx2K
30fps 240Mbit/s ?)

But some 4.1 decoders are able to decode x264 produced 5.1 streams if
they respect all the 4.1 restrictions except the DPB size, which allows
to use 16 references. This is what Jason means I suppose.

> > The DPB size depends on the level.
> 
> Did I say anything else ?
> 
> You must understand that hardware manufacters will target a level and 
> adjust any hardware requirements to it as closely as possible, in order 
> to reduce the cost. A hardware decoder supporting SD at most, but 16 
> refs on SD, ought not exist ( I'm not affirmative, because there are 
> crazy people out there... )

I agree with you here. This is why it is better in my opinion that x264
by default limit itself to level 3.0 if SD pictures are encoded. And it
should also limit to 4.1 if HD is encoded. Unless the users requires a
higher level by asking for more references.

This is why I support Loren's patch.

Best regards
-- 
Loïc

"heaven is not a place, it's a feeling"
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