On 10/31/18 6:16 AM, Dan Dennedy wrote:
On Tue, Oct 30, 2018 at 3:54 PM Daniil V. Kolpakov <d...@progmeistars.lv
<mailto:d...@progmeistars.lv>> wrote:
Hello! I was told on the kdenlive mailing list that I might have better
luck asking this on mlt-devel.
I'm using the latest Kdenlive/mlt on Arch Linux.
I've found that adding a color channel mixer effect, even with default
settings, changes pixel values to broadcast range (16-235). Adding
another Colorchannelmixer on top of it compresses the levels further to
28-223, and so on.
[...]
I reproduced it. This is a bug in the MLT libavfilter adapter due to
limitations between FFmpeg and MLT, but the colorchannelmixer is one of
the rare avfilters that only operates in RGB, which is when this problem
appears. The limitations are MLT does not support the yuvj422p pixel
format, and FFmpeg does not support yuvj422 (which MLT can support).
As a result, this bug appears whenever the downstream MLT component
requests a YUV image instead of RGB because libavfilter does a RGB to
YUV conversion at MPEG (broadcast) ranges. Thus, a simple workaround is
to add the frei0r squareblur (with size 0) after the colorchannelmixer.
This has very low overhead. I do not have a code fix yet; I have to
learn more about libavfilter.
Thanks a lot for the workaround, at least it's usable now!
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