[FFmpeg-devel] [PATCH 2/2] lavc/libaomenc: Support lossless encoding

[Ryo Hirafuji]

> So "crf 0" already has a meaning different from all other crf values?

No. "crf 0" has the same meanings. It just makes the quality better than
"crf 1".

I read libaom again, and I apologize for my wrong explanation:
  I found that if certain conditions are met, "crf 0" also generates
lossless videos.

If these conditions are not met, "-crf 0" will be lossless:

<<FFmpeg options>>
  "-bit_rate 0" (which means, enccfg.rc_end_usage = AOM_Q)
  "-aq-mode none"
  "-enable_restoration 0"

<<the libaom settings which can't be configured from FFmpeg yet>>
  AV1E_SET_ENABLE_CHROMA_DELTAQ must be 0
  AV1E_SET_ENABLE_SUPERRES must be 0

Thus, at least, "-lossless" does have a different meaning from "-crf 0",
so I think it would be useful to add "-lossless" flags.


2020年4月4日(土) 19:29 Carl Eugen Hoyos <ceffmpeg at gmail.com>:

> Am Sa., 4. Apr. 2020 um 12:16 Uhr schrieb Ryo Hirafuji
> <ryo.hirafuji at link-u.co.jp>:
> >
> > > Is it possible to use "cfr 0" instead?
> >
> > Unfortunately, crf=0 is not lossless.
> > "lossless" flag uses "quantisation matrices", which is different from the
> > default quantizer determined by "-crf", to achieve lossless encoding.
>
> So "crf 0" already has a meaning different from all other crf values?
>
> Thank you, Carl Eugen
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