libavformat/movenc.c:3209: error: Uninitialized Value
  The value read from first[_] was never initialized.

libavformat/movenc.c:3209:32: 
3207.             if (enabled[i] > 1)
3208.                 mov->per_stream_grouping = 1;
3209.             if (!enabled[i] && first[i] >= 0)
                                     ^
3210.                 mov->tracks[first[i]].flags |= MOV_TRACK_ENABLED;
3211.             break;
