Baptiste Coudurier wrote:
On 12/06/2009 08:12 AM, Vitor Sessak wrote:
Hi and sorry for the delay.
Artur Bodera wrote:
On Tue, Dec 1, 2009 at 12:50 AM, Vitor Sessak <vitor1...@gmail.com>
wrote:
While I normally oppose making non-committed code more complex, I think
this feature is so often requested that it is worth the extra work in
the
future. Stefano, Michael, any strong opinion about this?
I think the vf_overlay should be modified altogether. Although
mathematically alpha-blending is more expensive than opaque pixel
replacement, I think that it should be automatically decided by
analyzing
the overlay format.
So the alpha-blending should be a "built-in" functionality (not a
switchable
parameter) and should be implicitly functional with any overlay
stream/image
that has alpha channel (i.e. rgba). If there is no alpha channel, then
pixel
overriding would be used. This makes much more sense.
I agree that this would be nice, but there is no way to make it work
with the current format negotiation in libavfilter. For example, there
is no way to have a filter that accepts either "input: rgb, output rgba"
or "input: yuv, output: yuva", so I suggest you just do as your present
patch for the time been.
How much harm does doing yuv -> yuva or rgb -> rgba in all cases ?
To my knowledge it would only be a matter of adding one component and
memset it to 0xff.
This wouldn't do much harm, but there is no way of asking for such kind
of inputs in lavfi (i.e., either "rgb,rgba" or "yuv,yuva"). And changing
lavfi to accept such constraints would probably make colospace
negotiation a NP problem.
-Vitor
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