Good question, JB :-)
The composite transition gives less image quality for alpha blending due to
subsampled chroma. This also introduces a 2-pixel precision limitation,
which is bad enough on its own but even worse for animation. I was
basically doing some future-proofing for animation support and to let the
user choose a blending mode, which you can do now by selecting a track and
using Properties. It does support frame threaded parallel processing, which
can help; but currently Shotcut only exposes that in non-realtime mode
(including export). I have not been happy with performance either, but
still Shotcut only has one track transition choice. So, I chose the one
with best quality and flexibility.
On Wed, Jul 13, 2016 at 3:19 PM Jean-Baptiste Mardelle <j...@kdenlive.org>
wrote:
> Hi all,
>
> I have a question regarding multitrack compositing in video editors using
> MLT. In Shotcut, you add a freir.cairoblend transition to ensure
> transparency between tracks.
>
> I copied this approach for Kdenlive, but this leads to a huge performance
> loss (maybe because the freir.cairoblend transition only handles RGBA
> format):
>
> Trying to play a single HD clip with a freir.cairoblend transition, I get a
> maximum of 16 fps on my core i7.
>
> Replacing the freir.cairoblend transition with MLT's builtin composite
> transition, I can play at 50 fps without problem.
>
> The problem gets worse when you have several tracks, each one having its
> transition.
>
> So my question is why did you decide to use the frei0r.cairoblend
> transition over MLT's composite... is there anything preventing using
> composite ?
>
> Thanks and take care.
>
> jb
>
>
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