BibEncode: updated for latest BibDocFile APIs

* Compatibility with new BibDocFiles APIs introduced
  with commit e8e870c.

Signed-off-by: Jerome Caffaro <jerome.caffaro@cern.ch>
Tested-by: Tibor Simko <tibor.simko@cern.ch>
BibEncode: support for FFmpeg >= v0.9

* Updated encoding parameters for recent FFmpeg versions,
  and dropped default support for older versions.

Signed-off-by: Jerome Caffaro <jerome.caffaro@cern.ch>
Tested-by: Tibor Simko <tibor.simko@cern.ch>