Cannot merge videos

[pvnam198]

• I am using the below code to merge videos

    val commandList = ArrayList<String>()
  
    val contentFilterComplex = StringBuilder()
  
    inputFiles.forEachIndexed { index, file ->
        commandList.add("-i")
        commandList.add(file.absolutePath)
        contentFilterComplex.append("[$index:v][$index:a]")
    }
    contentFilterComplex.append("concat=n=${inputFiles.size}:v=1:a=1[v][a]")
    commandList.add("-filter_complex")
    commandList.add(contentFilterComplex.toString())
    commandList.add("-map")
    commandList.add("[v]")
    commandList.add("-map")
    commandList.add("[a]")
    commandList.add(outputFile.absolutePath)
  
    val arr = Array(commandList.size) { i -> commandList[i] }
  
    FFmpegCmd.exec(
        arr,
        duration * Util.MICROSECOND,
        object : OnEditorListener {
            override fun onSuccess(): Boolean {
                onExecCmdListener.onSuccess(outputFile)
                return false
            }
  
            override fun onFailure() {
                onExecCmdListener.onFailure()
            }
  
            override fun onProgress(progress: Float) {
                onExecCmdListener.onProgress(progress)
            }
        })
  

• Command log: -i input_1.mp4 -i input_2.mp4 -filter_complex [0:v][0:a][1:v][1:a]concat=n=2:v=1:a=1[v][a] -map [v] -map [a] my_output.mp4

• Error: E/AVLOG: Invalid file index 1 in filtergraph description [0:v][0:a][1:v][1:a]concat=n=2:v=1:a=1[v][a].

• Pls help me