AnimeMusicVideos.org

if subtitles are hard-coded MKVToolNix is not going to help you;
if subtitles are soft-coded it's (usually) pointless effort to explicitly remove them using this or any other tool;

stand-alone VirtualDub shouldn't be able to handle mkv. Not without FFMpeg Input Plugin (FFInputDriver) or some Matroska plugin;
=> I would try peeking inside plugins32/64 folder;

hint:. start by investigating the preview panel of AE.
RAM preview: link
CTI: link

for importing both video and audio track, you can try doing:

It is expected seeking would be slow using 0. Instead of dss update ffms2 (currently 2.20) and this time try without setting seekmode manually or use 1, i.e default mode);
else: see if LSMASHVideoSource (for .mp4's) performs faster.
~ probably threre is no need for ConvertToYV12

Watatashi wrote:FFVideoSource("The Giver.mkv")

you have to load audio track as well:

looks just like a regular spam of Twitch plugin from VCP.
using slide and light etc operators (and with the 'RGB split' enabled for the slide on the second example). some audio react probably too.
but it is possible to create effect manually as well.

VirtualDub

most likely you are intending to use Adobe's Dynamic Link feature.

for 10-bit encodes. (which most likely you have) you need to convert instead of recontainering source files. (i.e jump to section B)