VLC Player is a free, open-source video player that can play any video format. It can also convert your video files into the MP4 format. You can download VLC from videolan.org. It is available for any OS. This will launch the conversion tool. Add... button and select the video. You can load videos of almost any format. Click Convert / Save once you've selected your file(s). This will tell VLC to convert the file into the MP4 format. You can click the Settings button to adjust the settings. Most users can leave them at default. Browse... button and save the output file. This will be the final converted file. Make sure you name it something you'll recognize. Start button and wait. The conversion process will take as long as the original video. This is because VLC plays the video and re-records it as MP4.

TL;DR in Indonesian:
Unduh dan pasang VLC Player. Klik menu "Media" di VLC Player, lalu pilih "Convert / Save". Klik tombol . Pilih "Video – H.264 + MP3 (MP4)" dari menu "Profile". Klik tombol . Klik tombol .