Better quality for video editor previews

Currently, the encoding profiles for the video editor previews generate a quite bad quality where various compression artefacts are obvious.

This has several drawbacks:

• Misleads non-technical users assuming that the publications will be as bad as the preview
• Cannot use previews to assess quality of the recording

Of course, increasing the quality of the video editor previews will result in larger files for the previews. On the other hands, those can be retracted (or re-created) anytime.