[FFmpeg-user] Fade in filter and alpha channel fade in text

[Michael Koch]

Am 13.08.2018 um 10:08 schrieb Joshua Grauman:
>>> Hi all,
>>>
>>> I am combining various effects, and I noticed that when I fade in a 
>>> video
>>> using the [in]fade=t=in:st=2:n=24[out] syntax, and I fade in text using
>>> alpha='if(lt(t,2),0,if(lt(t,3),t-2,1))', that they both fade in 
>>> roughly at
>>> the same time, but both are not linear. I'm guessing the fade=in uses a
>>> sine wave or something to fade in the video, while clearly the text 
>>> fade
>>> is based on a linear fading of the alpha channel. Am I correct that the
>>> video fade in is a sinusoidal fade? Does anyone know offhand how I 
>>> could
>>> get the text fade to match the video one?
>>
>> Fade is always linear in this filter.
>
> Good to know, obviously I have something else wrong then. Thanks!

Well, if you are using both fading methods simultaneously, then the text 
has a quadratic fading curve.
because in the middle of the fading interval you have a factor 0.5 from 
the fade filter, and also a factor 0.5 from the alpha function. 0.5 * 
0.5 = 0.25.

Michael