I asked whether there's any better software than Handbrake for the job. How to compress my original large videos to small size in the most efficient way
Most transcoder GUIs use ffmpeg as the backend (including Handbrake), so the actual software doesn't matter, the settings do. As for what settings are best, it's highly dependent on several factors, including:
- Source resolution and bitrate
- How static the video is
- Noise/grain in the video
- Common occurrence when lighting is less than ideal, especially with older cameras
- Fineness of detail that needs to be preserved
- This would be influenced by how the videos were shot: recorded from a regular height and flipped page by page like in document scanning, or up close moving down each page, or something else
It's therefore difficult to say what would be ideal as I don't know what the source looks like, especially since this is far from a common use case. As I mentioned before, you can start by switching to the x265 encoder, reducing the framerate to a divisor of the original (eg. 60fps to 30fps to 15fps), and changing the encoder preset to the slowest you can tolerate. You can leave the CRF at 22 (if source is 1080p, 18 if lower) to start with and check if it's preserving the detail you need, and go from there. Be aware that if your source files are 1080p and in the range of 30-40MB/minute (i.e. 4-6Mbps) you may not be able to reduce the file size much without losing detail. Also be sure to test your settings across multiple different samples to ensure they scale well to your entire dataset.
Finetuning all of these things can take hours or even days (depending on encode time and dataset size), and that's before getting into more resource intensive codecs like AV1 or preprocessing filters and so on - this is why I suggested alternate storage options. And to be frank, using video to do backups seems like a less efficient and less effective method compared to the photographs you've taken, and I can't imagine a context where those would be less valid than video taken by (presumably) the same camera at the same time, especially if altered metadata is acceptable; that said, it's your workflow, your choice. If you do transcode it all, I strongly recommend keeping a backup of the originals on local storage - burn them to a few DVDs, copy them to a couple of flash drives, anything.
P.S. You can also use try the 10 bit version of the x265 encoder, since you can sometimes get better results even for 8 bit content, but you may run into compatibility issues with Google Photos and/or certain devices.