Unable to find a suitable output format for ffmpeg android

Question

This is the command. I am trying to merge audio into video.

val tempFile = File(requireActivity().cacheDir, "output.mp4")
tempFile.createNewFile()
Log.e(TAG, ": " + tempFile.length())

val command: String = "ffmpeg \\\n" +
        "    -i $video \\\n" +
        "    -i $audio \\\n" +
        "    -c:v copy \\\n" +
        "    -c:a copy \\\n" +
        "    -shortest \\\n" +
        "    -f mp4 \\\n" +
        "    ${tempFile.absolutePath}"

The command becomes:

ffmpeg \
                                                                                                    
-i /data/user/0/com.rohaitas.example/cache/temp_video.mp4 \
                                                                                                    
-i /data/user/0/com.rohaitas.example/cache/temp_audio.mp3 \
                                                                                                    
-c:v copy \
                                                                                                    
-c:a copy \
                                                                                                    
-shortest \
                                                                                                    
-f mp4 \
                                                                                                    
/data/user/0/com.rohaitas.example/cache/output.mp4

[NULL @ 0xb4000076a3da3b00] Unable to find a suitable output format for 'ffmpeg' ffmpeg: Invalid argument

Dependency implementation 'com.arthenica:ffmpeg-kit-full:5.1'

Command failed with state COMPLETED and rc 1.null
Stream #1:0
Audio: mp3, 48000 Hz, stereo, fltp, 199 kb/s
Metadata:
encode: 
Lavc59.18
[NULL @ 0xb4000076a6f4ec80] Unable to find a suitable output format for 'ffmpeg'
ffmpeg: Invalid argument

Answer 1

Just managed to Fixed the issue, Now it doesn't give error.

 val tempFile = File(requireActivity().cacheDir, "output.mp4")
 tempFile.createNewFile();
    
 val command= StringBuilder()
 .append("-y") //overWrite
 .append(" -i ").append(video)  // video
 .append(" -i ").append(audio)  // audio
 .append(" -c:v ").append("copy")
 .append(" -c:a ").append("copy")
 .append(" -shortest ") // shortest from both
 .append(" -f ").append("mp4 ")
 .append(tempFile.absolutePath)


val session = FFmpegKit.execute(command.toString())