Blender Git Loki

Fix #28949: can't render video to Flash

Several issues were discovered when was looking into this bug:

- MPEG file format didn't set needed codec settings such as frame
rate and so, Was caused by not very correct fix fix #21351.
- "Expert" codec settings stored in idprops was affected on
formats which don't actually need them causing some conflicts
in codec settings.
- Flash codec doesn't support b-frames.

Now C presets shouldn't affect on each other and flash coded wouldn't
use b-frames even when using h264 format. Should work fine for files
created from scratch. If existing files fails to render, try to
switch file format to something else and then back to needed value.