无人机拍摄的视频增加实时高度信息

• 一、工具准备
• 二、操作步骤
• • 1. 导出视频中的位置信息
  • 2. 使用Java将位置信息转换为srt
  • 3. 视频+字幕合并（ffmpeg）
• 参考材料

1. exiftool，用于导出视频的GPS信息（包括海拔高度）
   下载地址：https://exiftool.org/
2. ffmpeg，给视频增加字幕
3. Java，将exiftool导出的位置文件转换为字幕文件srt

exiftool -p /path/to/gpx.fmt -ee xxx.MP4 >out.gpx
–gpx.fmt下载地址：
https://github.com/exiftool/exiftool/tree/master/fmt_files
out.gpx内容：

  {高度}
  {GPS时间}

public class SrtTest {
    private static final SimpleDateFormat EXIF_TIME_FORMAT = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss");
    private static final SimpleDateFormat SRT_TIME_FORMAT = new SimpleDateFormat("HH:mm:ss.mmm");
    public static void main(String[] args) throws IOException, ParseException {
        String exifFilePath = "xxx";
        List infoList = parseExifFile(exifFilePath);
        // 转换成字幕文件，保存到outputSrtFile
        String outputSrtFile="out.srt";
        transferToSrt(infoList,outputSrtFile);
    }
    private static void transferToSrt(List infoList,String outputFile) throws IOException, ParseException {
        File output = new File(outputFile);
        BufferedWriter fw = new BufferedWriter(new FileWriter(output,false));
        //1
        //00:00:00.000 --> 00:01:00.000
        //测试字幕
        Date videoStart = SRT_TIME_FORMAT.parse("00:00:00.000");
        infoList.sort(Comparator.comparing(o -> o.time));
        for(int i=1;i
            fw.write(i+"rn");
            long currTime = infoList.get(i).time.getTime();
            int displaySec = (int)(currTime-infoList.get(i-1).time.getTime())/1000;
            String process = buildTimeLine(videoStart,displaySec);
            fw.write(process+"rn");
            fw.write("高度:"+infoList.get(i).height+"rn");
            fw.write("rn");
            addDisplay(videoStart,displaySec);
        }
        fw.flush();
    }
    private static void addDisplay(Date videoStart,int displaySec){
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(videoStart);
        calendar.add(Calendar.SECOND,displaySec);
        videoStart=calendar.getTime();
    }
    //00:00:00.000 --> 00:01:00.000
    private static String buildTimeLine(Date videoStart,int displaySec){
        String process = SRT_TIME_FORMAT.format(videoStart)+" --> ";
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(videoStart);
        calendar.add(Calendar.SECOND,displaySec);
        process += SRT_TIME_FORMAT.format(calendar.getTime());
        return process;
    }
    private static List parseExifFile(String filePath) throws IOException, ParseException {
        List lines = Files.readAllLines(new File(filePath).toPath());
        Iterator iter = lines.iterator();
        List infoList = Lists.newArrayList();
        while(iter.hasNext()){
            String line = iter.next();
            if(line.contains("")){
                float height =Float.parseFloat(line.substring(line.indexOf("")+5,line.indexOf("")));
                System.out.println(height);
                String nextLine=iter.next();
                String timeStr= nextLine.substring(nextLine.indexOf("")+6,nextLine.indexOf(""));
                Date time = EXIF_TIME_FORMAT.parse(timeStr);
                System.out.println(time);
                infoList.add(new PosInfo(height,time));
            }
        }
        return infoList;
    }
    private static class PosInfo{
        float height;
        Date time;

        public PosInfo(float height, Date time) {
            this.height = height;
            this.time = time;
        }
    }
}

获得字幕信息，如下：

1
00:00:00.000 --> 00:00:01.000
高度:20.1

2
00:00:01.000 --> 00:00:02.000
高度:20.3

3
00:00:02.000 --> 00:00:03.000
高度:20.3

表示： 第0->1秒，字幕显示"高度:20.1"。

ffmpeg -i xxx.MP4 -vf subtitles=out.srt output.mp4

1. 视频文件信息导出，看回答。https://stackoverflow.com/questions/40333901/export-gps-points-from-dash-cam-with-ffmpeg
2. MP4合成字幕。https://www.jianshu.com/p/f33910818a1c