[FFmpeg-user] gif overlay miscalculating x and y, extra frame flash

[Michael Koch]

Am 10.02.2020 um 18:31 schrieb Michael Koch:
> Paul,
>>
>>> Nevertheless I have the same problem as the original poster, also 
>>> when I
>>> add :format=rgb. Something is wrong with the x,y calculations in the
>>> overlay filter. In my example I'm using sendcmd to set x and y. The
>>> coordinates are sometimes off by a few pixels. At the moment my command
>>> line is too complicated to show here. Give me a little bit of time to
>>> find an example that's easier to reproduce.
>> No, as already said if timebases and fps do not match you can not get
>> results you expect.
>> Use fps filter somehow...
>
> Here is a new example for unexpected behaviour of the overlay filter:
>
> c:\ffmpeg\ffmpeg -f lavfi -i testsrc2=size=hd1080:duration=10 -f lavfi 
> -i color=black:size=50x50:duration=7 -lavfi 
> "[1]sendcmd=f=test.cmd[2];[0][2]overlay=x=0:y=0:format=rgb" -t 10 -y 
> out.mp4
>
> The coordinates come from this test.cmd file:
>
> 0.0-1.0   overlay x 'lerp(1735-50,1723-50,t)',
>           overlay y 'lerp( 527-50, 529-50,t)';
> 1.0-2.0   overlay x 'lerp(1723-50,1605-50,t-1)',
>           overlay y 'lerp( 529-50, 526-50,t-1)';
> 2.0-3.0   overlay x 'lerp(1605-50,1440-50,t-2)',
>           overlay y 'lerp( 526-50, 526-50,t-2)';
> 3.0-4.0   overlay x 'lerp(1440-50,1266-50,t-3)',
>           overlay y 'lerp( 526-50, 523-50,t-3)';
> 4.0-5.0   overlay x 'lerp(1266-50,1113-50,t-4)',
>           overlay y 'lerp( 523-50, 523-50,t-4)';
> 5.0-6.0   overlay x 'lerp(1113-50,1007-50,t-5)',
>           overlay y 'lerp( 523-50, 522-50,t-5)';
> 6.0-7.0   overlay x 'lerp(1007-50, 966-50,t-6)',
>           overlay y 'lerp( 522-50, 522-50,t-6)';
> 7.0-8.0   overlay x 'lerp( 966-50, 964-50,t-7)',
>           overlay y 'lerp( 522-50, 522-50,t-7)';
> 8.0-9.0   overlay x 'lerp( 964-50, 964-50,t-8)',
>           overlay y 'lerp( 522-50, 522-50,t-8)';
> 9.0-10.0  overlay x 'lerp( 964-50, 964-50,t-9)',
>           overlay y 'lerp( 522-50, 522-50,t-9)';
>
> Please note that all movements end at 8s. No movement is specified 
> from 8s to 10s.
>
> In the command line I have two different durations, 10s for the main 
> video and 7s for the overlay.
> Expected behaviour would be that after 7s the last frame is used and 
> overlaid at the correct position.
> But it seems that sendcmd gets the wrong time, so that there is 
> movement visible until the end at 10s.

I just found my error myself. The sendcmd command is inserted at the 
wrong place in the filter chain. It must be inserted where the longer of 
the two inputs is.

Michael