In mplayer2, it was valid to try to start encoding before all streams
were initialized. mpv avoids this situation and thus allows us to
properly bail out on some kinds of failures.
Also, this commit fixes a missing check in ao uninit which could cause
heap corruption when ao initialization did not complete.
This allows to define which stream is to be used as first output stream.
This is useful because dvdauthor refuses VOB files where the audio
stream is the first stream.
When timestamps jump by more than 30 seconds, assume an unexpected
discontinuity. Fixes encoding aborts (i.e. no more frames written) at
DVD cell switches.
Stefano Pigozzi
Rudolf Polzer