user10560: How to correctly add expression to transparent background like on this question ffmpeg drawtext filter - create transparent background with text
for my case (where there are 3 lines in bottom right corner):
ffmpeg -i videoin.mp4 -vf "[in]drawtext=enable='between(t,2.5,6.5)':fontsize=50:fontcolor=White:fontfile='ariblk.ttf':text='textline1':x=min(4*(tw\+10)-(abs(4-2*(t-2.5)))*(tw+10)-tw\,10):y=h-th-130, drawtext=enable='between(t,2.5,6.5)':fontsize=50:fontcolor=White:fontfile='ariblk.ttf':text='textline2':x=min(4*(tw\+10)-(abs(4-2*(t-2.5)))*(tw+10)-tw\,10):y=h-th-75, drawtext=enable='between(t,2.5,6.5)':fontsize=50:fontcolor=White:fontfile='ariblk.ttf':text='textline3':x=min(4*(tw\+10)-(abs(4-2*(t-2.5)))*(tw+10)-tw\,10):y=h-th-20[out]" -codec:a copy videoout.mp4


user1871: Use the box options i.e. 
drawtext=enable='between(t,2.5,6.5)':fontsize=50:fontcolor=White:fontfile='ariblk.ttf':text='textline1':x=min(4*(tw\+10)-(abs(4-2*(t-2.5)))*(tw+10)-tw\,10):y=h-th-130:box=1:boxborderw=12:boxcolor=black@0.45

This adds a box with padding of 12 pixels around the text boundary, and the color is black with 45% opacity.
Using drawbox (add it before the drawtexts)
drawbox=y=ih-140:h=110:c=black@0.45:t=max:enable='between(t,2.5,6.5)'


Here's the entire vf expression:
-vf "drawbox=y=ih-140:h=110:c=black@0.45:t=max:enable='between(t,2.5,6.5)',drawtext=enable='between(t,2.5,6.5)':fontsize=50:fontcolor=White:fontfile='ariblk.ttf':text='textline1':x=min(4*(tw\+10)-(abs(4-2*(t-2.5)))*(tw+10)-tw\,10):y=h-th-130, drawtext=enable='between(t,2.5,6.5)':fontsize=50:fontcolor=White:fontfile='ariblk.ttf':text='textline2':x=min(4*(tw\+10)-(abs(4-2*(t-2.5)))*(tw+10)-tw\,10):y=h-th-75, drawtext=enable='between(t,2.5,6.5)':fontsize=50:fontcolor=White:fontfile='ariblk.ttf':text='textline3':x=min(4*(tw\+10)-(abs(4-2*(t-2.5)))*(tw+10)-tw\,10):y=h-th-20" -codec:a copy videoout.mp4


10560: <p>How to correctly add expression to transparent background like on this question <a href="https://video.stackexchange.com/questions/15551/ffmpeg-drawtext-filter-create-transparent-background-with-text">ffmpeg drawtext filter - create transparent background with text</a>
for my case (where there are 3 lines in bottom right corner):</p>

<pre><code>ffmpeg -i videoin.mp4 -vf "[in]drawtext=enable='between(t,2.5,6.5)':fontsize=50:fontcolor=White:fontfile='ariblk.ttf':text='textline1':x=min(4*(tw\+10)-(abs(4-2*(t-2.5)))*(tw+10)-tw\,10):y=h-th-130, drawtext=enable='between(t,2.5,6.5)':fontsize=50:fontcolor=White:fontfile='ariblk.ttf':text='textline2':x=min(4*(tw\+10)-(abs(4-2*(t-2.5)))*(tw+10)-tw\,10):y=h-th-75, drawtext=enable='between(t,2.5,6.5)':fontsize=50:fontcolor=White:fontfile='ariblk.ttf':text='textline3':x=min(4*(tw\+10)-(abs(4-2*(t-2.5)))*(tw+10)-tw\,10):y=h-th-20[out]" -codec:a copy videoout.mp4
</code></pre>
 1871: <p>Use the box options i.e. </p>

<pre><code>drawtext=enable='between(t,2.5,6.5)':fontsize=50:fontcolor=White:fontfile='ariblk.ttf':text='textline1':x=min(4*(tw\+10)-(abs(4-2*(t-2.5)))*(tw+10)-tw\,10):y=h-th-130:box=1:boxborderw=12:boxcolor=black@0.45
</code></pre>

<p>This adds a box with padding of 12 pixels around the text boundary, and the color is black with 45% opacity.</p>

<p>Using <strong>drawbox</strong> (add it before the drawtexts)</p>

<pre><code>drawbox=y=ih-140:h=110:c=black@0.45:t=max:enable='between(t,2.5,6.5)'
</code></pre>

<hr>

<p>Here's the entire vf expression:</p>

<pre><code>-vf "drawbox=y=ih-140:h=110:c=black@0.45:t=max:enable='between(t,2.5,6.5)',drawtext=enable='between(t,2.5,6.5)':fontsize=50:fontcolor=White:fontfile='ariblk.ttf':text='textline1':x=min(4*(tw\+10)-(abs(4-2*(t-2.5)))*(tw+10)-tw\,10):y=h-th-130, drawtext=enable='between(t,2.5,6.5)':fontsize=50:fontcolor=White:fontfile='ariblk.ttf':text='textline2':x=min(4*(tw\+10)-(abs(4-2*(t-2.5)))*(tw+10)-tw\,10):y=h-th-75, drawtext=enable='between(t,2.5,6.5)':fontsize=50:fontcolor=White:fontfile='ariblk.ttf':text='textline3':x=min(4*(tw\+10)-(abs(4-2*(t-2.5)))*(tw+10)-tw\,10):y=h-th-20" -codec:a copy videoout.mp4
</code></pre>
