[FFmpeg-trac] #9132(ffmpeg:open): Wrong pixel format/output when converting video to yuv444p*

FFmpeg trac at avcodec.org
Thu Mar 25 01:17:51 EET 2021

#9132: Wrong pixel format/output when converting video to yuv444p*
             Reporter:  viley       |                    Owner:
                 Type:  defect      |                   Status:  open
             Priority:  important   |                Component:  ffmpeg
              Version:  git-master  |               Resolution:
             Keywords:  regression  |               Blocked By:
             Blocking:              |  Reproduced by developer:  1
Analyzed by developer:  0           |

Comment (by JEEB):

 Replying to [comment:8 Balling]:
 > Replying to [comment:7 JEEB]:
 > > Alright, this seems to be an issue in the scale filter not overriding
 color metadata properly in case of a pixel format conversion :) Thus the
 issue itself is much older, but it just never popped up until my change
 started passing the information further.
 > Or maybe because by default it uses libx264 and not -c:v libx264rgb?

 I am not sure what that is a reference to? The encoder selection (and thus
 which `pix_fmt` is selected by default as the output of the video filter
 chain) is outside the scope of both:

 1. my changes to ffmpeg.c (to actually pass on information provided by the
 filter chain onwards), as well as
 2. the issue identified in the `scale` video filter in this ticket.

 Or would you say that f.ex. RGB→YCbCr conversion should still preserve the
 color space value of `gbr` in the output AVFrame? :) (which is only there
 due to there being a `av_frame_copy_props` call, which copies all the
 metadata from the input AVFrame - which is not filtered afterwards
 depending on whether it was just a scale job, or if the pix_fmt was
 changed, etc etc)

 To fix the `scale` filter bug there needs to be some logic added to not
 pass on input metadata as-is in case of a conversion that would nullify
 it, such as conversion from YCbCr to RGB or vice versa.

Ticket URL: <https://trac.ffmpeg.org/ticket/9132#comment:9>
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