While merge multiple videos how can we add transition between them?

[vandanabpatel]

Can you please help me out i wand to add transition between videos
i want to achive something like this
https://www.youtube.com/watch?v=INiRu2_XdJE
https://www.youtube.com/watch?v=V-lL1MTPkSQ

fun mergeWithFade() {

    if (videos == null || videos!!.isEmpty()) {
        callback!!.onFailure(IOException("File not exists"))
        return
    }

    for (v in videos!!) {
        if (!v.canRead()) {
            callback!!.onFailure(IOException("Can't read the file. Missing permission?"))
            return
        }
    }

    val outputLocation = getConvertedFile(outputPath, outputFileName)

    val inputCommand = arrayListOf<String>()

    //Add all paths
    for (i in videos!!) {
        inputCommand.add("-i")
        inputCommand.add(i.path)
    }
    //Apply filter graph
    inputCommand.add("-filter_complex")

    //Compose concatenation commands
    val stringBuilder = StringBuilder()

// stringBuilder.append("[1:v][0:v]blend=all_expr='A*(if(gte(T,3),1,T/3))+B*(1-(if(gte(T,3),1,T/3)))'[v0];");

    for (i in 0 until videos!!.size) {
        val fade = Constant.DURATION_FADE_TRANSITION;

        val mp = MediaPlayer.create(context, Uri.fromFile(videos!!.get(i)))
        val duration = mp.duration / 1000
        mp.release()
        val startDuration = duration - fade;

        stringBuilder.append("[$i:v]fade=type=out:duration=" + Constant.DURATION_FADE_TRANSITION + ":start_time=" + startDuration + ",setpts=PTS-STARTPTS,setsar=1,scale='min(480,iw)':min'(320,ih)':force_original_aspect_ratio=decrease,pad=480:320:(ow-iw)/2:(oh-ih)/2[v$i]; [$i:a]afade=type=out:duration=" + Constant.DURATION_FADE_TRANSITION + ":start_time=" + startDuration + ",asetpts=PTS-STARTPTS[a$i];");
    }

    for (i in 0 until videos!!.size) {
        stringBuilder.append("[v$i][a$i]")
    }

    // Concat command
    stringBuilder.append("concat=n=${videos!!.size}:v=1:a=1[v][a]")

    //Complete Command
    val cmd = arrayOf<String>(
            "-map",
            "[v]",
            "-map",
            "[a]",
            "-preset", //Presets can be ultrafast, superfast, veryfast, faster, fast, medium (default), slow and veryslow.
            "ultrafast", //Using a slower preset gives you better compression, or quality per file size.
            "-crf", //Constant Rate Factor
            "23", //Value from 0 to 51, 23 is default, Large Value for highest quality
            outputLocation.path,
            "-y" //Overwrite output files without asking
    )

    val finalCommand = (inputCommand + stringBuilder.toString() + cmd).toTypedArray()

    try {
        FFmpeg.getInstance(context).execute(finalCommand, object : ExecuteBinaryResponseHandler() {
            override fun onStart() {}

            override fun onProgress(message: String?) {
                callback!!.onProgress(message!!)
            }

            override fun onSuccess(message: String?) {
                refreshGallery(outputLocation.path, context)
                callback!!.onSuccess(outputLocation, OutputType.TYPE_VIDEO)

            }

            override fun onFailure(message: String?) {
                if (outputLocation.exists()) {
                    outputLocation.delete()
                }
                callback!!.onFailure(IOException(message))
            }

            override fun onFinish() {
                callback!!.onFinish()
            }
        })
    } catch (e: Exception) {
        callback!!.onFailure(e)
    } catch (e2: FFmpegCommandAlreadyRunningException) {
        callback!!.onNotAvailable(e2)
    }
}