Why Transcoding won’t increase Quality

The misunderstanding comes from confusions about capturing vs transcoding. Capturing at a higher bit depth is pretty much always a good thing for image quality. If you can capture at a higher bit depth, that’s great – go for it.

But if you are just transcoding from one codec to another, then the decision to encode to a higher-bit-depth codec (from 8-bit source to 10-bit output, for example) will not improve the image at all. It probably won’t hurt, but it also won’t help.

Source: https://blog.frame.io/2017/08/16/increasing-bit-depth/