[Jim Eidt] “How do you re-acquire SD footage within a timeline, while changing its aspect ratio from 4:3 to 16:9? I only want to do that to some of the footage, which was originally captured in the wrong aspect ratio. It’s a complicated timeline, so I really don’t want to start from scratch. Or maybe I could conform the individual clips in the timeline, but that option doesn’t appear in the menus. Thanks for any thoughts.”
Does that mean you have a 16:9 timeline with 4:3 footage incorrectly scaled to 16:9 in it? All material in a timeline is in the same aspect ratio (at least Media 100 does think that), so some of your footage most likely is wrongly flagged either as 4:3 or as 16:9.
Now, if you have 4:3 clips in a 16:9 timeline here is what you can do:
Copy your 4:3 clip from your 16:9 timeline, paste it into a 4:3 timeline. The system will ask hwo to handle the 16:9->4:3 conversion, where you choose “Change aspect ratio”. Now your clip has the correct 4:3 aspect ratio.
Copy the clip back from your 4:3 timeline into your 16:9 timeline, and when the conversion dialog pops up, this time use the “Conform Media” command with the settings you want to use. There needs to be some conversion from 4:3->16:9, and maybe you have to try some different settings to see which one is good for you.