The VideoLAN Forums

Every time when I wanna download anime videos, I would check its videos' details first before I start downloading them.
I don't want AC3 videos, but sometimes when there was no choice.

Most animes that are available in the interent
usually come with different video formats:
Some of them were ripped as MKV of AC3 audio,
while some as AVI of MP3 audio.
When I played the videos which audio parts are composed of MP3 in VLC, and I turned the volume to half of its maximum level, the loudness was about to break my eardrums; but for the same level of volume, I couldn't hear clearly when playing videos of AC3 audio in VLC even if I have increased the value of Gain.

Why did they choose AC3 instead of MP3 when ripping the videos?
I couldn't think of any advantages of AC3 over MP3 offhand?

Fifty percent volume in VLC is 100% in most other players and VLC has 6 dB of gain form 50% to 100% which is double the gain. AC3 is typically 8 dB lower in gain than MP3 or DTS.

As to what the differences are and why people prefer one over the other is a topic for lots of discussion, history of the formats and purpose for the formats. This is altogether to long to go into here. Of coarse the most obvious reason would be stereo versus surround sound (5.1).