I uploaded a 9.2GB file on my FileRun install; it worked as expected, up until the uploaded finished.
FileRun is reporting the file as 1.1GB; no idea where this value is from, since when I look on the filesystem, I can see the .upload file increase in size during the upload, up to 9.2GB, and the final file is indeed 9.2GB.
Trying to watch the .mp4 file in question from my FileRun install, it stops at around 10%, and downloading it from FileRun results in a 1.1GB file. But the file is OK on the filesystem; I even did a checksum, and it's the same for the local and uploaded file.
Here's a screen capture of the file being uploaded: https://photos.app.goo.gl/SjTSFeC1r7BL5aWN9
I uploaded other large files with similar results: a 7.2GB file appears as 3.2GB in FileRun; another 6.1GB file appears as 2.1GB in FileRun, 7.8GB => 3.7GB, etc.
OS: Raspbian (Debian 9 Stretch on Raspberry Pi 3 armv7l)
FileRun version : 2018.11.11
PHP version: 7.0.27
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