Creating AVI's with AC-3 (Dolby Digital) sound

It is possible to have 5.1 AC-3 sound (Dolby Digital) multiplexed in an AVI file. With the appropriate setup, these AVI-AC3 files can be played normally in any video player based on DirectShow (most players). At playback time, you can also decide whether you want the AC-3 sound to be decoded and played on your computer speakers (2, 4 or 6) or to be pass-through via your S/PDIF (digital) output so that you can hook an external AC-3 decoder for full 5.1 surround restitution. This can be useful to keep the original AC-3 soundtrack on your DVD backups.

1. Getting the video file and the AC3 file
2. Multiplexing the AVI and AC3 files
3. Enable AVI-AC3 playback on your system
4. Configuring the AC-3 processing

1. Getting the video file and the AC3 file

First, you need to have your video file and the associated AC3 file stored separately. If your source is a VOB file, for example, you need to convert the video part to AVI format and demux the right AC3 track. You can check for information on this site if you do not know how to do that.

2. Multiplexing the AVI and AC3 files

Next, you have to use a modified version of VirtualDub, named "VirtualDub AC3", to multiplex the AC3 sound into the AVI. To start with, open the video-only AVI file.

Then you have to select the audio source as external WAV audio.

When asked for a WAV file, choose to display All files (*.*) and select your AC-3 file.

If the AC-3 file is valid and if you have the right version of VirtualDub ("VirtualDub AC3"), you will get the following message:

This message is informing you about the properties of the selected AC-3 stream.

Next, you can choose a compressor for the video (like DivX) and save you AVI file as you normally do with VirtualDub. Be sure to not change "Direct Stream Copy" for the audio.

The resulting AVI file has AC-3 audio multiplexed in it. All properties are retained, as you can see when you right-click on it in the Explorer and you view the "Summary" tab:

3. Enable AVI-AC3 playback on your system

This step only needs to be done the first time. You must install two Active Movie filters to enable AVI-AC3:

• mpgaudio.ax
• iviaudio.ax

To install mpgaudio.ax : get the filter from our download page (in audio) and copy the file in your windows' system directory (\windows\system on win9x/ME or \winnt\system32 on Windows 2000 Professional).