FFmpeg 4 support.

• Video can (sometimes) continue when there is an error in the video stream.
  • This is useful for webcams that are not completely standards compliant.
• Video now works with FFmpeg 4.
  • Hopefully also with the infrastructure to make future upgrades easier.
• Default Video quality much higher for mp4 files.
• Add L-cut and J-cut functions to base API.
• Add remove-video and remove-audio filters to base API.
• Add a volume filter.
• More work on live streaming. Some initial testing for windows.
• Updare libvid, seems to work on windows now.