MainActivity.java

package com.slowvideoc;

import com.arthenica.mobileffmpeg.Config;
import com.arthenica.mobileffmpeg.FFmpeg;

import android.Manifest;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.provider.MediaStore;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.util.Log;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;

import java.io.File;
import java.util.Timer;
import java.util.TimerTask;

public class MainActivity extends AppCompatActivity {
    private static final int SELECT_VIDEO = 1001;
    private static final int PERMISSIONS_REQUEST_READ_EXTERNAL_STORAGE = 1002;
    private static final int PERMISSIONS_REQUEST_WRITE_EXTERNAL_STORAGE = 1003;

    private Timer timer;
    public native void run(String[] argv);

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        FloatingActionButton fab = findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                startActivityForResult(
                    new Intent(Intent.ACTION_PICK, MediaStore.Video.Media.EXTERNAL_CONTENT_URI),
                    SELECT_VIDEO);
            }
        });

        if (checkSelfPermission(Manifest.permission.READ_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
            requestPermissions(new String[]{Manifest.permission.READ_EXTERNAL_STORAGE},
                    PERMISSIONS_REQUEST_READ_EXTERNAL_STORAGE);
        }
        if (checkSelfPermission(Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
            requestPermissions(new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},
                    PERMISSIONS_REQUEST_WRITE_EXTERNAL_STORAGE);
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        if (resultCode != RESULT_OK) {
            return;
        }
        if (requestCode == SELECT_VIDEO) {
            String path = getPath(data.getData());
            if (path != null) {
                convert(path);
            } else {
                snack("Can't locate the file");
            }
        }
    }

    private String getPath(Uri uri) {
        String[] projection = { MediaStore.Video.Media.DATA };
        Cursor cursor = getContentResolver().query(uri, projection, null, null, null);
        if (cursor != null) {
            int index = cursor.getColumnIndexOrThrow(MediaStore.Video.Media.DATA);
            cursor.moveToFirst();
            return cursor.getString(index);
        }
        return null;
    }

    private void snack(String message) {
        Snackbar.make(findViewById(R.id.main_activity), message, Snackbar.LENGTH_LONG).show();
    }

    private void convert(String path) {
        File file = new File(path);
        if (!file.exists()) {
            snack("File not found: " + path);
            return;
        }
        int index = path.lastIndexOf(".");
        String outputPath = new StringBuilder(path).replace(index, index + 1, "_.").toString();
        int code = FFmpeg.execute(String.format(" -i \"%s\" -vcodec libx264 -preset slow -acodec aac \"%s\"", path, outputPath));
        if (code != 0) {
            snack("Failed with code " + code);
        } else {
            snack("Started, now wait, it's sloow...");
        }
    }

    public void startTimer() {
        timer = new Timer();
        TimerTask timerTask = new TimerTask() {
            @Override
            public void run() {
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        int rc = FFmpeg.getLastReturnCode();
                        String output = FFmpeg.getLastCommandOutput();
                        if (rc == FFmpeg.RETURN_CODE_SUCCESS) {
                            Log.i(Config.TAG, "Command execution completed successfully.");
                        } else if (rc == FFmpeg.RETURN_CODE_CANCEL) {
                            Log.i(Config.TAG, "Command execution cancelled by user.");
                        } else {
                            Log.i(Config.TAG, String.format("Command execution failed with rc=%d and output=%s.", rc, output));
                        }
                    }
                });
            }
        };
        timer.scheduleAtFixedRate(timerTask, 0, 1000);
    }
}