Cannot play .mp4 videos with the default video player

I downloaded some .mp4 videos on my PC and I want play them on my Samsung Galaxy Ace 2. Despite the .mp4 videos can be played in my PC1 *(with no problem)*, in my device *(using the predefined video media player)* the video cannot be played. This screenshot shows the videos that my device cannot play them: Only the video *(pointed with the green arrow)* - which is the default video that my device has can be played. When I select any of the other videos, the device says: "Content not supported": Each time I send the video *(via cable from the PC to the device)*, it will show two options: Do you wish convert (insert_video_name_here.mp4) before copy it to the device? - Yes, convert and copy *(recommended)*. - No, just copy *(File will copy, but it might be possible it cannot play in the device)*. No matter which option I select, the video is not playable. This is the information about the predefined app: I was reading this answer and this one too about similar problems, but what I understand is due the resolution of the video, but I have no idea what can I do for play these videos in my device *(despite those videos are .mp4 or .wmv files "the same as the predefined video - pointed with the green arrow in a previous screenshot")*. I really don't want download another app and play the videos with them, hence I ask: How can be played those videos wth the predefined app? ---------- 1 Windows 7 Professional 32 bits. Using Google Chrome "as video player" and the Windows Media Player. PS: I also read about software which can convert videos for device-compatibility, but I'm not sure if those are free-malware applications.