[FFmpeg-trac] #8455(undetermined:new): libaom-av1 damages brightness range by switching yuvj420p to yuv420p

[FFmpeg]

#8455: libaom-av1 damages brightness range by switching yuvj420p to yuv420p
-------------------------------------+-------------------------------------
             Reporter:  john123      |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:
  undetermined                       |  unspecified
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 Summary of the bug: libaom-av1 reduces brightness range by switching
 yuvj420p to yuv420p
 How to reproduce: encode a yuvj420p input using libaom-av1

 The downgrade of quality is listed as a warning as per below, although the
 implication is not at all clear unless you research the difference between
 them:
 {{{
 Incompatible pixel format 'yuvj420p' for codec 'libaom-av1', auto-
 selecting format 'yuv420p'
 }}}

 And indeed the help shows yuvj420p is not supported.

 In the head of github source there is a AV_PIX_FMT_YUVJ420P defined, but
 it's not allowed in av1_pix_fmts etc. Is this intentional? It makes AV1
 rather damaging for a yuvj420p input that has a lot of very dark and very
 bright pixels.

 Not sure if I should try to patch in AV_PIX_FMT_YUVJ420P or not... If
 there's some reason that libaom-av1 is fundamentally incompatible with
 yuvj420p, it seems at least ffmpeg should recommend some alternative that
 doesn't result in a degraded output.

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Ticket URL: <https://trac.ffmpeg.org/ticket/8455>
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