ffmpeg - inacurate overlay position

Question

I am trying to add two overlays using ffmpeg as below:

[v0][1:v] overlay=21:24:enable='between(t,0.000, 1.135)' [v1];
[v1][2:v] overlay=120:24:enable='between(t,0.000, 1.135)' " 

These two images [1:v] and [2:v] are below pngs:

The first png is 99px wide and I want to place it on x=21

The second png I want to place right behind the first one x=21+99=120

But I am getting the output as below: It seems that there is 1px gap between them and I have no idea where is it coming from.

How can I ensure it is pixel perfect and there is no gap?

Also I noticed that if the image is 98px and I use:

[v0][1:v] overlay=21:24:enable='between(t,0.000, 1.135)' [v1];
[v1][2:v] overlay=119:24:enable='between(t,0.000, 1.135)' " 

then suprisingly it is fine, same for 100px wide and next images x=121

The whole command to give more context (remove newlines to execute):

.\bin\ffmpeg.exe -ss 0 -to 5.681 
-i C:\Users\Radoslaw\Videos\ttt.mp4 
-i .\tempAssets\player1.png 
-i .\tempAssets\serving.png 
-filter_complex 
[0:v] select='between(t,1.247,2.550)+between(t,4.181,5.681)', setpts='PTS-STARTPTS-((gt(T,2.550)*1.630))/TB' [v0]; 
[0:a] aselect='between(t,1.247,2.550)+between(t,4.181,5.681)', asetpts='PTS-STARTPTS-((gt(T,2.550)*1.630))/TB'; 
[v0][1:v] overlay=21:21:enable='between(t,0.000, 2.803)' [v1];
[v1][2:v] overlay=120:21:enable='between(t,0.000, 2.803)' 
Untitled.mp4

@Gyan your answer helped for the mentioned simple scenario but if I change the order:

[v0][2:v] overlay=120:24:enable='between(t,0.000, 1.135)':format=auto,format=yuv444p [v1];
[v1][1:v] overlay=21:24:enable='between(t,0.000, 1.135)' " 

then I get the 1px gap again. Any suggestions?

Answer 1

Change base video to full chroma sampling and try.

[0:v] select='between(t,1.247,2.550)+between(t,4.181,5.681)', setpts='PTS-STARTPTS-((gt(T,2.550)*1.630))/TB',format=yuv444p[v0];

and

[v0][1:v] overlay=21:21:enable='between(t,0.000, 2.803)':format=auto,format=yuv444p [v1];
[v1][2:v] overlay=120:21:enable='between(t,0.000, 2.803)'