[FFmpeg-devel] Once again: Multithreaded H.264 decoding withffmpeg?

Jason Garrett-Glaser darkshikari
Sat May 31 01:00:04 CEST 2008

> The 'problem' that most people run into with decoders that are
> restricted to L4.1 is that most content on the internet today use lots
> of reference frames and b-pyramid (which essentially counts as 2
> reference frames) and the Decoded Picture Buffer for L4.1 limits you
> to 4 refs at 1080P (2 if your use b-pyramid which then is essentially
> useless) and 8 refs (IIRC) at 720P. Usually it's not a bitrate problem
> as bitrate for L4.1 is sufficiently high.

If I recall correctly, x264 defines the number of reference frames by
DPB size, meaning that "4 reference frames" uses 4 reference frames
for P-frames, 4 reference frames for B-frames (3 L0, 1 L1), and 4 for
B-pyramid B-frames (2 L0, 2 L1).  Most encoders I know of do something
similar.  The vast majority of consumer-created HD rips (read: piracy)
are going to be compliant if they've been encoded with a recent x264,
since most rippers don't use that many refs.  Anime is a different
story, since more refs is actually very useful there and encoders tend
to use larger numbers (though they don't generally use 1080p either!)

The main problem with L4.1 is just that the level flag is set to 5.1 ;)

Dark Shikari

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