There are a few different ways to concatenate two videos in Android. Here is one approach you could use:

First, you will need to use a video editing library to open and decode the video files. There are several options available for this, including FFmpeg and MediaCodec.

Next, you will need to create a new video file and encode the frames from the two input videos into the new file. You can do this using a video encoding library such as FFmpeg or MediaCodec.

Finally, you will need to write the encoded frames to the new video file using a file output stream.

Here is some example code that demonstrates how to use FFmpeg to concatenate two videos in Android:

String[] cmd = {"-i", inputFile1, "-i", inputFile2, "-filter_complex", "[0:v:0][0:a:0][1:v:0][1:a:0]concat=n=2:v=1:a=1", "-ab", "48000", "-ac", "2", "-ar", "22050", "-s", "640x480", "-vcodec", "mpeg4", "-b", "2097152", "-r", "30", "-y", outputFile};
FFmpeg.getInstance(context).execute(cmd, new ExecuteBinaryResponseHandler() {
    @Override
    public void onSuccess(String message) {
        // Video concatenation successful
    }

    @Override
    public void onFailure(String message) {
        // Error occurred while concatenating videos
    }
});

This code will concatenate the two input videos (inputFile1 and inputFile2) and write the result to the output file (outputFile). You can customize the encoding options by adjusting the parameters passed to FFmpeg.