[FFmpeg-trac] #2701(avcodec:open): mpeg2video 4:2:2: green artefacts at the bottom with lowres 3

[FFmpeg]

#2701: mpeg2video 4:2:2: green artefacts at the bottom with lowres 3
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             Reporter:  ami_stuff    |                    Owner:
                 Type:  defect       |                   Status:  open
             Priority:  normal       |                Component:  avcodec
              Version:  git-master   |               Resolution:
             Keywords:  mpeg2video   |               Blocked By:
  lowres                             |  Reproduced by developer:  1
             Blocking:               |
Analyzed by developer:  1            |
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Changes (by michael):

 * analyzed:  0 => 1


Comment:

 This is 4:2:0 not 4:2:2 and 4:2:0 interlaced with 240 lines has 16
 invissible lines, they are all green i assume. with lowres these 16 (4 per
 chroma field) get mixed with the vissible ones as the 8 line block that
 contains 4 green lines is just one pixel at lowres 3.
 Thus in some sense its expected to have a green last line.
 Could this be worked around, yes but its not pretty requireing to detect
 this specific case and calculate the IDCT differently.
 Does this affect any real world use cases ?

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Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/2701#comment:2>
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