public VoiceHint getVoiceHint(int i) {
        if (voiceHints == null) {
            return null;
        }
        for (VoiceHint hint : voiceHints.list) {
            if (hint.indexInTrack == i) {
                return hint;
            }
        }
        return null;
    }
writes the track in binary-format to a file

@param filename the filename to write to
main/src/main/java/cgeo/geocaching/brouter/core/OsmTrack.java