Currently it is impossible to preserve "raw" data streams when streaming out of VLC. People have been asking about this for nearly a decade:
* https://forum.videolan.org/viewtopic.ph ... 7&p=194158
* https://forum.videolan.org/viewtopic.ph ... 5&p=308648
* https://forum.videolan.org/viewtopic.ph ... 1&p=337238
* https://forum.videolan.org/viewtopic.ph ... 4&p=405598
VLC doesn't have to "support" KLV, it just has to include the raw bits from the input stream when generating output. `ffmpeg` has done this for years.