[feature/privacy] Streaming removal of Exif data from mp4 files

[tsmethurst]

Currently we remove Exif data tags (except rotation and alpha-channel data) from images using exif-terminator. However, we don't have a good way of removing exif data from mp4 videos yet. This has privacy implications, since Exif data can contain location information if that setting is enabled on the device which took the video, and the video has not been reencoded or scrubbed by the user already.

To make it easier for users to avoid leaking location metadata, we should look at updating exif-terminator to also allow removal of Exif metadata from mp4 file types, and update GoToSocial to pass mp4s through exif-terminator when media processing is performed.

Relevant terminator issue: https://codeberg.org/superseriousbusiness/exif-terminator/issues/9

[daenney]

It turns out this apparently uses QuickTime or XMP tags, and there's multiple of the fuckers that can contain location info

• https://exiftool.org/TagNames/QuickTime.html
• https://exiftool.org/TagNames/XMP.html

There's a bajillion location related tags.

[daenney]

Matroska spatial information tags only do country-level tags it seems: https://www.matroska.org/technical/tagging.html. Haven't found any official docs on encoding coordinates in it.

[tsmethurst]

Starting to understand why people just reencode the whole video file :')