user33223: Usually, you can use this command to open a video with a subtitle in VLC, if it isn't detected automatically:
vlc.exe path_to_video.mp4 --sub-file path_to_sub.srt
But I want to open multiple videos, each with their own subtitle file. How do I do that?
Neither vlc.exe video1.mp4 video2.mp4 --sub-file sub1.srt sub2.srt
nor vlc.exe video1.mp4 --sub-file sub1.srt video2.mp4 --sub-file sub2.srt seem to work.

user29988: This is a workaround which converts the files to another container format. It happens almost as fast as your hard disk can write data because nothing is re-encoded.

use MKVToolNix (specifically mkvmerge) to combine the mp4 files and their srt files into mkv files (perhaps you can automate this with a loop). I never use this tool via command line and cannot tell you the exact command, but you'll find more information here https://mkvtoolnix.download/doc/mkvmerge.html
use vlc.exe *.mkv afterwards.

Maybe this question helps too https://superuser.com/questions/609113/how-to-add-and-remove-subtitles-in-an-mkv-file which should also work with an mp4 file as input.

33223: <p>Usually, you can use this command to open a video with a subtitle in VLC, if it isn't detected automatically:<br />
<code>vlc.exe path_to_video.mp4 --sub-file path_to_sub.srt</code></p>
<p>But I want to open multiple videos, each with their own subtitle file. How do I do that?<br />
Neither <code>vlc.exe video1.mp4 video2.mp4 --sub-file sub1.srt sub2.srt</code><br />
nor <code>vlc.exe video1.mp4 --sub-file sub1.srt video2.mp4 --sub-file sub2.srt</code> seem to work.</p>
 29988: <p>This is a workaround which converts the files to another container format. It happens almost as fast as your hard disk can write data because nothing is re-encoded.</p>
<ol>
<li>use MKVToolNix (specifically mkvmerge) to combine the mp4 files and their srt files into mkv files (perhaps you can automate this with a loop). I never use this tool via command line and cannot tell you the exact command, but you'll find more information here <a href="https://mkvtoolnix.download/doc/mkvmerge.html" rel="nofollow noreferrer">https://mkvtoolnix.download/doc/mkvmerge.html</a></li>
<li>use <code>vlc.exe *.mkv</code> afterwards.</li>
</ol>
<p>Maybe this question helps too <a href="https://superuser.com/questions/609113/how-to-add-and-remove-subtitles-in-an-mkv-file">https://superuser.com/questions/609113/how-to-add-and-remove-subtitles-in-an-mkv-file</a> which should also work with an mp4 file as input.</p>
