www.makemkv.com

So weirdly something Iv'e never had a problem with when I put an mkv in to remove things such as audio, languages and certain subs the speed is literally a crawl now. I know this is a new problem as I downgraded to 1.17.6 and things were working great and flying through now thats is impossible since my. mac update they no longer work, 1.18.1 is seemingly extremely slow with certain reads like almost to a crawl upwards of 40 min for a 20 gb file it would take like 3 min at most usually any ideas?

If you already have a mkv with subs/audio that you don't want the easiest and quickest way to remove them is with MKVToolNix.

Does it make any difference if you're reading or writing to/from internal storage vs external storage?

bmillham is right to suggest MKVToolNix as a useful tool in many situations.