There is no encryption on Freeview. It's the stream as broadcast that is recorded.
I've never had a problem playing a recording with vlc on a Linux desktop. And I've just copied an HD file over to my Android phone - it' still going fine after 15 mins.
By this, do you mean that you have copied these files onto the et8500 from elsewhere, and they have problems on the et8500?
You're using FTP for the file transfer. Have you set it to binary transfer mode? If you're doing it in text mode then the copy will be incorrect in places, and may well show the symptoms you describe.
I Played the recordings using VLC on my windows laptop and then used an Android Media player using KODI and the same problems occurred.
The files was transferred from ET8500 using the move command on the box straight to another attached usb NTFS hard disk (no ftp) so I can play it on other media.
The media from other sources was on the NTFS hardisk which I connected to ET8500 Which had prblems playing them on the Android media player and my windows laptop these ather recording form various sources had no issues.
As mentioned I was not using FTP software, but used the button on the box in the media section /file explorer to move files to attached usb drive. So not sue where the binary bit comes in?