I don’t use VLC for video conversion – wish I could help you with personal experience on that issue. I use Adobe Premiere Pro CC or Adobe Media Encoder CC for conversions. I used to use Vegas Pro for conversions. And for someone who might be willing to experiment, DaVinci Resolve 15 has a free version that might help you out, but that’s probably also overkill for this task. I know there are numerous smaller utilities out there that will do something similar for conversion purposes. I just can’t personally vouch for them so I’ll defer to other folks’ experience on good third-party conversion tools besides Adobe or full-featured video editing programs.