user21908: I overlay using the following command:
ffmpeg -i video.mp4 -i logo.png -filter_complex "[1]geq=r='r(X,Y)':a=0.1[a];[0][a] overlay=x='if(gte(t,2), -w+(t-2)*20, NAN)':y=0" out.mp4

I tried adjusting the opacity using 
fmpeg -i video.mp4 -i logo.png -filter_complex "[1]format=rgba,geq=r='r(X,Y)':a='1*alpha(X,Y)'[a];[0][a] overlay=x='if(gte(t,2), -w+(t-2)*20, NAN)':y=0" out.mp4

but it is still transparent at the white color part.
It seems like the white color part has a transparency of 0, causing the second command to not work.
Is there any reason why this is happening? The logo I tried is 

How can I preserve the white color?

user1871: There is no white color. That's the background color of the page showing through. Your input PNG is palettized 8-bit image where black color indicates transparency.
Apply the following filter to the image to convert black pixels to white and set a uniform transparency.
geq=r='if(p(X,Y),p(X,Y),255)':g='if(p(X,Y),p(X,Y),255)':b='if(p(X,Y),p(X,Y),255)':a=0.1


21908: <p>I overlay using the following command:</p>

<pre><code>ffmpeg -i video.mp4 -i logo.png -filter_complex "[1]geq=r='r(X,Y)':a=0.1[a];[0][a] overlay=x='if(gte(t,2), -w+(t-2)*20, NAN)':y=0" out.mp4
</code></pre>

<p>I tried adjusting the opacity using </p>

<pre><code>fmpeg -i video.mp4 -i logo.png -filter_complex "[1]format=rgba,geq=r='r(X,Y)':a='1*alpha(X,Y)'[a];[0][a] overlay=x='if(gte(t,2), -w+(t-2)*20, NAN)':y=0" out.mp4
</code></pre>

<p>but it is still transparent at the white color part.</p>

<p>It seems like the white color part has a transparency of 0, causing the second command to not work.</p>

<p>Is there any reason why this is happening? The logo I tried is </p>

<p><a href="https://i.stack.imgur.com/dMICv.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/dMICv.png" alt="enter image description here"></a></p>

<p>How can I preserve the white color?</p>
 1871: <p>There is no white color. That's the background color of the page showing through. Your input PNG is palettized 8-bit image where black color indicates transparency.</p>

<p>Apply the following filter to the image to convert black pixels to white and set a uniform transparency.</p>

<pre><code>geq=r='if(p(X,Y),p(X,Y),255)':g='if(p(X,Y),p(X,Y),255)':b='if(p(X,Y),p(X,Y),255)':a=0.1
</code></pre>
