Mixed editing of 8bit and 10bit files

Premiere internally processes in 32-bit float. So ... an 8-bit clip is converted mathematically into 32-bit float, just as is a 10 or 12 bit file. The program doesn't care about the differences. But more bit depth in the clip means more data for the program to work with.

That's the working pipeline. (A colorist term, but useful.)

The image sent to the monitor depends on the bit space of the file being viewed at this moment. Sort of. (It's a complicated discussion to completely cover ... and yes, I have dealt with that in published works.) This is another 'pipeline'.

The export depth of the file will be what you choose to do. There are presets built that are in format/codec likely to be 8-bit, some that will more likely be 10 bit.

You can set the export to be 10 bit via the options in the Export process.

However ... exporting an 8 bit file in a 10 bit export does not magically get more data into the file. It simply 'spreads' the data over those 10 bits.

So back to your question for a timeline with mixed 8 and 10 bit files, a very common occurence.

If you export with 10 bit settings, the exported file, the file itself, will be fully 10 bit. But ... there will be more image data for those images that are 10 bit than for the sections that were 8 bit. More likely to get say banding in the sections of the file from an 8 bit original clip.

Neil