On 03.08.2018 19:46, Dan Dennedy wrote:
On Fri, Aug 3, 2018 at 10:23 AM Jean-Baptiste Mardelle
<j...@kdenlive.org <mailto:j...@kdenlive.org>> wrote:
Hi all,
I recently realized that the color producer always creates an alpha
mask, and uses the rgba24a format by default.
Typically, it will receive a format from the downstream consumer
services, and it will only choose this default if movit is used or
mlt_image_none is received.
Hi Dan,
Thanks for your answer.
In fact, unless the color has an alpha value under 255, it is
unnecessary and we could simply use an rgb24 format, saving some
memory.
I am mostly interested in this because the qtblend transition
checks if
a producer has an alpha channel before deciding whether a
compositing is
required. Having a useless alpha channel on the color producer causes
unnecessary compositing and slowdowns in this case. Would you be
ok to
change the color producer to use rgb24 or rgb24a formats depending on
the alpha value ?
Only in the truly default case. If qtblend requests mlt_image_rgb24a
and the color producer returns mlt_image_rgb24, then the image
conversion filter will automatically convert it. That is slightly less
efficient than directly returning what is requested.
Ok, I realize I didn't correctly analyze the situation. You are totally
right that in most cases, the format will be determined by the consumer
services.
In fact, the optimization would be to only create the alpha mask if the
consumer requests an rgba format or if the alpha is less than 255.
something like:
+ uint8_t *alpha = NULL;
+ if (color.a < 255 || *format == mlt_image_rgb24a) {
+ alpha = mlt_pool_alloc( alpha_size );
+ (...)
If the consumer requests yuv4222 and the color has no transparency, it
doesn't make sense to create an alpha mask ?
For frei0r.cairoblend, I check every pixel's alpha until it sees one
that is not 255. See transition_frei0r.c:is_opaque().
Sure but it seems to me that simply checking for the presence of an
alpha mask would be much faster than checking every pixel of a frame..
Thanks & regards
Jean-Baptiste
I can provide a patch if you think this is a welcome change.
Best regards
Jean-Baptiste
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