[FFmpeg-devel] [PATCH] lavfi: add fade filter

[Stefano Sabatini]

On date Tuesday 2011-02-22 04:53:13 +0100, Michael Niedermayer encoded:
> On Mon, Feb 21, 2011 at 10:22:00PM +0100, Stefano Sabatini wrote:
> > On date Monday 2011-02-21 18:06:50 +0100, Michael Niedermayer encoded:
[...]
> > > fade=in:10:20,fade=out:50:60
> > > could be supported as:
> > > fade=in:10:20:50:60
> > > 
> > > and
> > > fade=out:10:20:50:60
> > > to black a part out (currently not supported with individual filters easily)
> > > 
> > > and more than 2, that is N such fade in/outs in a single filter would also be
> > > usefull
> > > for example consider that someone concatenates videos from several scenes to
> > > make a movie. She might want to create fade out+fade in at the transitions
> > 
> > Uhm, so it may support a list:
> > fade=out=S:D;in=S:D;out=S:D;...
> 
> fade=out=S:D:S:D:S:D:...
> doesnt need escaping and is shorter
> you cant have 2 out or 2 in after each other so this is not ambigous syntax

What about having two distinct fade and multifade filters?

My problem with the multifade is that allowing #F and time format
creates problems since it isn't possible to reliably predict the exact
timing of a duration expressed using a number of frames, so you could
have fade-in/fade-out intervals overlap or nesting.

On the other hand I reckon that using frames for expressing init and
end of a fade-in/out could be useful, and is not problematic for a
single fade.

So we could have:
fade={in|out}=TIMEINT
fade={in|out}=TIMEINT

TIMEINT::= S+D | S-E

(S=Start, D=Duration, E=End)

where S, D, and E can be expressed both as a number of frame (#F, with
F a number of frames) or TIME (where time is parsed by
av_parse_time()).

For the multi-fade:
fade={in|out}=TIMEINT{:[{in|out}=]TIMEINT}*

but with TIMEINT not supporting the #F syntax.

The following in|out are optional, but may help redability:
in=TIMEINT:out=TIMEINT:in=TIMEINT:out=TIMEINT
rather than:
in=TIMEINT:TIMEINT:TIMEINT:TIMEINT

Another possibility would be to drop the #F syntax, and have just one
fade filter.
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