Hi,
try to burn a 1.2GB mp4 film onto a DVD or as iso to a foulder. Result only about 200MB a burned (readable) to the DVD and the source file of 1.2GB is cut also to about 200MB (same size as shown on DVD), the size of the burned 1.2GB film varied in 2 trials from about 80MB to about 200MB. To check wether it's my system or not, I made a new installation of F27, same error. F26 does not show this error ( brasero-3.12.1-5.fc26 )

- brasero-3.12.2-2.fc27
- Name         : kernel
  Version      : 4.15.4
  Release      : 300.fc27
  Arch         : x86_64

First Time I see this in Brasero
Kind regards