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

[Carl Eugen Hoyos]

Am Sa., 4. Apr. 2020 um 13:17 Uhr schrieb Ryo Hirafuji
<ryo.hirafuji at link-u.co.jp>:
>
> > 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".

That was my question, sorry for being unclear.

> 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.

In an ideal world, crf 0 would force all other settings for a lossless
encoding.

Carl Eugen