diff --git a/app/src/main/java/com/frank/ffmpeg/activity/VideoHandleActivity.kt b/app/src/main/java/com/frank/ffmpeg/activity/VideoHandleActivity.kt
index 75131ba..30e8233 100644
--- a/app/src/main/java/com/frank/ffmpeg/activity/VideoHandleActivity.kt
+++ b/app/src/main/java/com/frank/ffmpeg/activity/VideoHandleActivity.kt
@@ -53,6 +53,9 @@ class VideoHandleActivity : BaseActivity() {
     private var list :List<String> ?= null
     private var isJointing = false
 
+    private var firstSrcFile: String = ""
+    private var selectingSecondFile = false
+
     @SuppressLint("HandlerLeak")
     private val mHandler = object : Handler() {
         override fun handleMessage(msg: Message) {
@@ -295,17 +298,25 @@ class VideoHandleActivity : BaseActivity() {
                 commandLine = FFmpegUtil.videoToImage(srcFile, mStartTime, mDuration, mFrameRate, outputPath)
             }
             12 -> { //combine into picture-in-picture video
-                val inputFile1 = PATH + File.separator + "beyond.mp4"
-                val inputFile2 = PATH + File.separator + "small_girl.mp4"
-                if (!FileUtil.checkFileExist(inputFile1) && !FileUtil.checkFileExist(inputFile2)) {
-                    return
+                // NOTE: The first video should be bigger than the second one.
+                if (selectingSecondFile) { // User has selected 2 files
+                    selectingSecondFile = false
+                    if (!FileUtil.checkFileExist(firstSrcFile) && !FileUtil.checkFileExist(srcFile)) {
+                        showToast("请选择两个源文件")
+                        return
+                    }
+                    //x and y coordinate points need to be calculated according to the size of full video and small video
+                    //For example: full video is 320x240, small video is 120x90, so x=200 y=150
+                    //val x = 200
+                    //val y = 150
+                    outputPath = PATH + File.separator + "PicInPic.mp4"
+                    commandLine = FFmpegUtil.picInPicVideoInCorner(firstSrcFile, srcFile, 2, outputPath)
+                } else {
+                    firstSrcFile = srcFile
+                    selectingSecondFile = true
+                    showToast("画中画：请再选择一个文件")
+                    selectFile() // pop up to select another source file
                 }
-                //x and y coordinate points need to be calculated according to the size of full video and small video
-                //For example: full video is 320x240, small video is 120x90, so x=200 y=150
-                val x = 200
-                val y = 150
-                outputPath = PATH + File.separator + "PicInPic.mp4"
-                commandLine = FFmpegUtil.picInPicVideo(inputFile1, inputFile2, x, y, outputPath)
             }
             13 -> { //playing speed of video
                 outputPath = PATH + File.separator + "speed.mp4"
diff --git a/app/src/main/java/com/frank/ffmpeg/util/FFmpegUtil.java b/app/src/main/java/com/frank/ffmpeg/util/FFmpegUtil.java
index 9406f1f..7262420 100644
--- a/app/src/main/java/com/frank/ffmpeg/util/FFmpegUtil.java
+++ b/app/src/main/java/com/frank/ffmpeg/util/FFmpegUtil.java
@@ -638,6 +638,32 @@ public class FFmpegUtil {
         return insert(pipVideo.split(" "), 2, inputPath1, 4, inputPath2, outputPath);
     }
 
+    /**
+     * convert videos into picture-in-picture mode
+     *
+     * @param whichCorner 0: top-left; 1: top-right; 2: bottom-left; 3: bottom-right
+     * @return convert success or not
+     */
+    public static String[] picInPicVideoInCorner(String inputPath1, String inputPath2, int whichCorner, String outputPath) {
+        String pipCmd = "ffmpeg -i -i -filter_complex ";
+        switch (whichCorner) {
+            case 1:
+                pipCmd += "overlay=W-w";
+                break;
+            case 2:
+                pipCmd += "overlay=0:H-h";
+                break;
+            case 3:
+                pipCmd += "overlay=W-w:H-h";
+                break;
+            case 0:
+            default:
+                pipCmd += "overlay";
+                break;
+        }
+        return insert(pipCmd.split(" "), 2, inputPath1, 4, inputPath2, outputPath);
+    }
+
     /**
      * move moov box in the front of mdat box, when moox box is behind mdat box(only mp4)
      *