//创建字幕轨道
		RMVPMediaVideoBlendItem *blendItem1 = [[RMVPMediaVideoBlendItem alloc] initWithBlendMode:RMVPMediaVideoBlendModeNormal];

        subtitleTrack = [[RMVPMediaVisibleTrack alloc] initWithBlendItem:blendItem1];

        subtitleTrack.trackId = kBDMVMediaVisibleSubtitleTrackId;

        [self.videoTrack addVideoTrack:subtitleTrack];
		//添加字幕片段
        RMVPMediaTextSegment *subtitleSegment = [[RMVPMediaTextSegment alloc] init];

        [subtitleTrack addSegment: subtitleSegment];


		//配置字幕与预览实时显示
		 CGFloat videoWidth = self.previewer.previewConfig.width;

   		 CGFloat videoHeight = self.previewer.previewConfig.height;

    	[self.videoTrack setupSubtitleStyleWithPreviewSize:CGSizeMake(videoWidth, videoHeight)];

	//获取字幕轨道中字幕片段
	RMVPMediaTextSegment *textSegment = [self.videoTrack subtitleSegment];
	
	//设置字幕内容，获取媒体轨道中心当前时间
    CMTime currentTime = self.previewer.cursor.cursorTime;


	//新增字幕
	if (!currentItem) {

        currentItem = [[RMVPMediaTextItem alloc] init];

        currentItem.mainText = self.tmpMainTitle;

        currentItem.subText = self.tmpSubTitle;

        RMVPMediaTextItem *nextTextItem = nil;

        NSArray *textAllItems = [textSegment textAllItem];

        for (RMVPMediaTextItem *tmpItem in textAllItems) {

            CMTimeRange timeRange = tmpItem.timeRange;
            if (CMTimeCompare(timeRange.start, currentTime) > 0) {
                nextTextItem = tmpItem;
                break;
            }
        }

        CGFloat newSubtitleDuration = [BDMVEditSubtitleSettings sharedInstance].addSubtitleDuration;

        if (newSubtitleDuration <= 0) newSubtitleDuration = 2;

        if (nextTextItem) {

            CMTime eventualDuration;

            CMTime nextItemStartTime = nextTextItem.timeRange.start;

            CMTime gapTime = CMTimeSubtract(nextItemStartTime, currentTime);

            if (CMTimeCompare(gapTime, CMTimeMake(newSubtitleDuration, 1)) >= 0) {
                eventualDuration = CMTimeMake(newSubtitleDuration, 1);
            } else {
                eventualDuration = gapTime;
            }

            currentItem.timeRange = CMTimeRangeMake(currentTime, eventualDuration);

            NSInteger index = [textSegment textIndexAtRefTime:nextItemStartTime];
			//插入字幕到指定位置
            [textSegment insertTextAtIndex:index item:currentItem];

            [self.subtitleEditManager.seekBarAera insertSubtitleAtIndex:index];

        } else {

            CMTime eventualDuration;

            CMTime mediaDuration = self.tracksCenter.userTrack.trackDuration;

            CMTime remainingDuration = CMTimeSubtract(mediaDuration, currentTime);

            if (CMTimeCompare(remainingDuration, CMTimeMake(newSubtitleDuration, 1)) >= 0) {

                eventualDuration = CMTimeMake(newSubtitleDuration, 1);

            } else {

                eventualDuration = remainingDuration;

            }

            currentItem.timeRange = CMTimeRangeMake(currentTime, eventualDuration);
			//追加字幕
            [textSegment addTextWithItem:currentItem];

            [self.subtitleEditManager.seekBarAera addSubtitle];

        }
  
        NSInteger index = [textSegment textIndexAtRefTime:self.previewer.cursor.cursorTime];
		//更新字幕显示位置，详见[3.3.4 设置字幕画面位置]
        [self updateSubtitleDisplayAndRealSubtitlePositonWithTransition:SubtitleInitTranslation itemIndex:index];

    } else { // 编辑字幕

        currentItem.mainText = self.tmpMainTitle;

        currentItem.subText = self.tmpSubTitle;

        NSInteger index = [textSegment textIndexAtRefTime:currentTime];

        [self.subtitleEditManager.seekBarAera editSubtitleAtIndex:index];
    }

    //设置字幕显示位置
    currentFrame = self.displaySubtitleTextView.frame;//displayView的位置已经更新

    CGSize scale = [self currentVideoScale];

    BDMVPreviewTransform transform = self.subtitlePreviewTransform;

    CGFloat left = (CGRectGetMinX(currentFrame) - CGRectGetMinX(availabelRect) + Subtitle_InputView_OffsetX) / transform.scale;

    left += [self currentVideoInvisibleHorizontalPadding];

    CGFloat bottom = (CGRectGetMaxY(availabelRect) - CGRectGetMaxY(currentFrame) + Subtitle_InputView_OffsetX) / transform.scale;

    CGFloat right = (CGRectGetMaxX(availabelRect) - CGRectGetMaxX(currentFrame) + Subtitle_InputView_OffsetX) / transform.scale;

    right += [self currentVideoInvisibleHorizontalPadding];

    RMVPMediaTextSegment *currentSegment = [self.tracksCenter subtitleSegment];

    NSDictionary *attributes = @{@"marginBottom":@(bottom * scale.height),

                                 @"marginLeft":@(left * scale.width),

                                 @"marginRight":@(right * scale.width)};

    [currentSegment updateStyleAtIndex:index styleAttributes:attributes];