avconv.c:2847: error: Uninitialized Value
  The value read from sync_stream_idx was never initialized.

avconv.c:2847:17: 
2845.             if (sync_file_idx >= 0) {
2846.                 m->sync_file_index   = sync_file_idx;
2847.                 m->sync_stream_index = sync_stream_idx;
                      ^
2848.             } else {
2849.                 m->sync_file_index   = file_idx;
