Vladislav Zharkov

I know I'm bumping an ancient thread, but I just recently ran into this exact issue, and it wasn't limited to just videos, but pretty much all file types, so I thought I'd share my solution. I was building a personal portfolio for a client and their website is hosted on DreamHost. Each time I uploaded a background video (8MB MP4 file) it would hang at 100% for a while, finish the upload and then show its size reduced to 2.5MB. Weirdly enough the video did play, but only a portion of it. This issue caught me off guard because I'm also running ProcessWire on a different hosting, and I've never encountered this problem before. I skimmed through phpinfo thinking that the upload limit was set too low, but it far exceeded the file size. I decided to upload a big image file (5MB JPG) somewhere in the gallery to see if it'll work, and the same issue happened. It got cut precisely at 2.5MB, thus getting corrupted, yet still displaying. So I decided to finally contact the support. Turns out it was ModSecurity acting aggressively, throwing the "Request body no files data length is larger than the configured limit" error. Support increased the limit and the issue was gone. So yeah, if anybody else ever encounters this problem, try increasing the ModSecurity file size upload limit.