user25024: I have used and installed AviSynth+ 64-bit on a machine. I then wanted to install AviSynth+ 32-bit to use the watermark filter. I followed these instructions to install 32-bit, changed the registry keys, and got a blue screen of death.
After a fresh reinstallation of the Windows system, I want to install 32-bit AviSynth+ only and avoid another blue screen of death.
On the new version 3.5.1 of AviSynth+, is XP the 32-bit version, or is any installer able to install a 32-bit version?

user18155: There is no problem with having installed both 32- and 64-bit version of AviSynth on your 64-bit machine, if you correctly placed 32-bit plugins vs. 64-bit ones to their appropriate places.
AviSynth is a frame server, it means, you never call it directly - other program call it back. It means that for example

64-bit Media Player Classic will call the 64-bit version of AviSynth,
32-bit Media Player Classic will call the 32-bit version of AviSynth.

Similarly

64-bit FFmpeg will call the 64-bit version of AviSynth,
32-bit FFmpeg will call the 32-bit version of AviSynth.

I guess that your problem lies in your FFmpeg installation — you have probably 64-bit, and it means that in the process of converting your .avs script to some media file the FFmpeg calls 64-bit version of AviSynth, and you need the 32-bit (because of your 32-bit filter).
So my advice is, install both 32- and 64-bit versions of FFmpeg (into different directories) and use the appropriate one for every particular case.

25024: <p>I have used and installed AviSynth+ 64-bit on a machine. I then wanted to install AviSynth+ 32-bit <a href="https://forum.videohelp.com/threads/396116-Adding-a-watermark-to-videos#post2574751" rel="nofollow noreferrer">to use the watermark filter</a>. I followed <a href="http://forum.doom9.org/showthread.php?t=172124" rel="nofollow noreferrer">these instructions</a> to install 32-bit, changed the registry keys, and got a blue screen of death.</p>

<p>After a fresh reinstallation of the Windows system, I want to install 32-bit AviSynth+ only and avoid another blue screen of death.</p>

<p>On <a href="https://github.com/AviSynth/AviSynthPlus/releases/tag/v3.5.1" rel="nofollow noreferrer">the new version 3.5.1 of AviSynth+</a>, is XP the 32-bit version, or is any installer able to install a 32-bit version?</p>
 18155: <p>There is no problem with having installed both 32- and 64-bit version of AviSynth on your 64-bit machine, if you correctly placed 32-bit plugins vs. 64-bit ones to their appropriate places.</p>

<p>AviSynth is a frame server, it means, you never call it directly - <em>other</em> program call it back. It means that for example</p>

<ul>
<li>64-bit Media Player Classic will call the 64-bit version of AviSynth,</li>
<li>32-bit Media Player Classic will call the 32-bit version of AviSynth.</li>
</ul>

<p>Similarly</p>

<ul>
<li>64-bit FFmpeg will call the 64-bit version of AviSynth,</li>
<li>32-bit FFmpeg will call the 32-bit version of AviSynth.</li>
</ul>

<p>I guess that your problem lies in your FFmpeg installation — you have probably 64-bit, and it means that in the process of converting your .avs script to some media file the FFmpeg calls 64-bit version of AviSynth, and you need the 32-bit (because of your 32-bit filter).</p>

<p>So my advice is, install both 32- and 64-bit versions of FFmpeg (into different directories) and use the appropriate one for every particular case.</p>
