I was recently asked about the benefits of transcoding AVCHD footage to ProRes 4:2:2 or 4:4:4.
AVCHD uses 4:2:0 subsampling, which is the same as MP4. Transcoding it to 4:4:4 or 4:2:2 won’t give you any more information than you had originally, but it will add less noise, if that makes sense.
The problem with transcoding is that, even if you’re transcoding to a higher-quality format, there’s always going to be data lost in translation. That’s one of the reasons I’ve switched from Final Cut to Premiere Pro … In Premiere, I can use the raw camera files from DSLR and AVCHD cameras like the Panasonic AF100 without having to transcode at all.
If you have no idea what I just said, please watch this video I made a couple of years ago to demystify the subject of chroma subsampling.
For a good example of what this looks like in real life, take a look at the 8:53 mark in this nice comparison video by OneRiverMedia of the Canon 5D Mark III and the Blackmagic Cinema Camera. It clearly shows how increased subsampling negatively affects the ability to key otherwise good-looking footage.