使用ffmpegFrameRecorder合并的视频很短？

Question

我正在使用JavaCV Api的ffmpegFrameRecorder将几个mp4视频合并为一个。这是我的代码：

FrameGrabber grabberlist[] = new FFmpegFrameGrabber[filenamelist
                    .size()];

for (int i = 0; i < grabberlist.length; i++) {

                System.out.println("FILES" + filenamelist.get(i));
                grabberlist[i] = new FFmpegFrameGrabber(filenamelist.get(i));
                grabberlist[i].start();

            }

            FrameRecorder recorder = new FFmpegFrameRecorder(
                    Environment.getExternalStorageDirectory()
                            + "/Apptavia/output.mp4",
                    grabberlist[0].getImageWidth(),
                    grabberlist[0].getImageHeight(), 1);

            recorder.start();

            for (int i = 0; i < grabberlist.length; i++) {

                Frame frame;
                while ((frame = grabberlist[i].grabFrame()) != null) {

                    recorder.record(frame);

                }
            }

            for (int i = 0; i < audioList.size(); i++) {

                recorder.record(audioList.get(i));
            }

            recorder.stop();

            for (int i = 0; i < grabberlist.length; i++) {

                grabberlist[i].stop();
            }
        }

创建输出视频但视频长度较短。我调试了.grab（）方法的帧数小于总帧数。什么可以解决这个问题。请帮忙。