[x265] Ghosting/artifacts even with low CRF

[Rômulo Silva]

This is related to issue #214:
https://bitbucket.org/multicoreware/x265/issues/214/ghosting-artefacts-even-with-low-crf-when


Turns out that it's easy to reproduce the problem with hardsubs, and I've
included both x264 and x265 samples below to illustrate this.


Lossless x264 sample:
http://www.mediafire.com/download/ftwysmcemw7211a/x264+crf0.mkv
Sample subtitle:
http://www.mediafire.com/download/jttvyk2k0va9c3g/lorem+ipsum.ass
x264 hardsub sample:
http://www.mediafire.com/download/nzp7pzz5y8h7yjy/hardsub_test_x264.mkv
x265 hardsub sample:
http://www.mediafire.com/download/mz51v2a8d99pa5t/hardsub+test.mkv


Both hardsub files were encoded with CRF 21, 10-Bit and slower preset. X265
encoder version was 1.9+150-00ea3784bd36.

You can clearly see the artifacts between the two lines on top of the left
book. Some ornaments get distorted around the letters, and straight edges
don't move according to the scene.

A few suggested workarounds, like --no-cutree, make the ghosting less
apparent, but it still doesn't solve the issue completely. I've included
below a sample of the same x265 encode used above (CRF 21, 10-Bit, slower)
with --no-cutree as the only additional parameter.


x265 hardsub sample [--no-cutree]:
http://www.mediafire.com/download/abvwr1jbp47uw29/hardsub_test_nocutree.mkv


The resulting file has over twice the size, and even though the artifacts
on ornaments are mostly gone, some straight edges in between the lines are
still not moving according to the scene.

Has any progress been made on this issue? I'm willing to help by providing
more samples and test cases, if needed.


Thanks for your attention,

R.S.
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