The reason is that there is no right AC3 codec installed on our Mac and so the default Mac QuickTime player or iTunes can not natively support AC3 audio. Three popular solutions are recommended to play AC3 on Mac. Solution One is to install the right AC3 codec. Solution Two is to convert the AC3 to QuickTime Player supported audio format. AC-3 ACM Codec is an AC3 ACM decoder. Install this and you can convert/decompress AC3 audio directly to WAV/MP3 using Virtualdub, Tmpgenc, etc. AC3 encoding support in latest versions. AC3 ACM Codec 2.2 Free Download - VideoHelp.

Ac3 Filter Codec Download
Gom Player Ac3 Codec Download Mac
Ac3 Codec Mac Download Windows 10

Ac3 Filter Codec Download

Gom Player Ac3 Codec Download Mac

Ac3 Codec Mac Download Windows 10

For sure that you have downloaded an avi video which seems to be without sound. It’s usual that they seem to be like that, but the real reason is that they include the sound codified using AC3 compression and you don’t have the correct codec installed.
This audio compression format is compatible with DolbySurround, Dolby ProLogic and Dolby ProLogic II and is more and more used. If you want to enjoy your videos with their sounds, install this codec and put no limits to your sound experience.
This DirectShow filter for AC3 is totally free and distributed under GNU license.