v0.25.3

• Upgrade video transcoding to v0.25.3
• Upgrade Handbrake to v1.3.3
• Upgrade FFMpeg to v4.3.1
• Upgrade x265 lib to v3.3
• Rebase onto Ubuntu 20.04
• Compile mp4v2 utils from source (no longer available as a package in Debian/Ubuntu)