[mythtv-commits] Ticket #12272: mythtranscode creating artifacts when transcoding interlaced mpeg2 streams

[MythTV]

#12272: mythtranscode creating artifacts when transcoding interlaced mpeg2 streams
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     Reporter:  tapperm@…               |      Owner:  jyavenard
         Type:  Bug Report - General    |     Status:  new
     Priority:  minor                   |  Milestone:  unknown
    Component:  MythTV - Mythtranscode  |    Version:  0.27-fixes
     Severity:  medium                  |   Keywords:
Ticket locked:  0                       |
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 I've been seeing issues with mythtranscode since approximately 0.23.
 Blocky artifacts are introduced around motion (especially where there is
 motion blur in the input stream). This was occurring even for ridiculously
 high bitrate and quality settings. Replicating the same bitrate, quality
 settings and flags in mythffmpeg did not result in the same artifacting,
 suggesting the problem may be caused something in mythtranscode or
 NuppelVideoRecorder.

 Applying deinterlace transcode filters does not have any effect on the
 problem - although different filters can exaggerate the problem.

 However, applying the postprocess filter or the ivtc filter fixes the
 problem completely - even though interlace combing is still left in the
 output stream.

 If deinterlace filters are applied before or after the postprocess or ivtc
 filters, the artifacts are reintroduced.

 Even more interestingly, applying the vflip filter generates extremely odd
 behaviour. The output from mythtranscode seems to show a mix of upside
 down and right-side up blocks in the same frame - possibly something is
 going on with the i-frames causing motion detected blocks to incorrectly
 reference the wrong field of an interlaced signal?

 Attached files:
 orig.mpg - original mpeg2 file.
 yadifdeint.nuv - yadif deinterlaced showing extreme artifacting
 kerneldeint.nuv - kernel deinterlaced showing less extreme artifacting
 vflip.nuv - vflipped version showing mixture of flipped and non-flipped
 blocks.
 postprocess.nuv - postprocess filtered. Still interlaced but no artifacts
 ivtc.nuv - inverse telecined - no artifacts
 ivtc-then-kerneldeint.nuv - deinterlaced after telecine, artifacts appear
 kerneldeint-then-ivtc.nuv - deinterlaced before telecine, artifacts
 present.

 Marking this as minor, since using ivtc filter seems to be an effective
 workaround. Postprocess would work, except that it has a tendency to
 segfault.

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Ticket URL: <https://code.mythtv.org/trac/ticket/12272>
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