That's a sorely needed function in AE and there's not really any easy way to do it that I'm aware of. I think it could be done with scripts and there are two scripts out there that could probably be combined
so that you could just select all of your footage layers, run the script and then just render out the trimmed footage to replace the long clips in your project.
The two scripts are Video Copilot's
Trim Compose script and
rd: Pre-compose from the redefinery.
The new script would need to be able to:
- Pre-comp the clips while trimming the comp and offering handle options
- Leave or move all attributes
- Correctly deal with clips that have time-remapping applied
- Make individual comps if multiple clips are selected
- Add the trimmed comps to the render queue
- Replace the trimmed comps with the rendered footage or set as a proxy for the comps in the render settings
Maybe someone with some scripting chops might have a go at it.