•  Windows 2000
•  Windows XP
•  Windows Vista

A large (and ever-increasing) percentage of the downloadable video on the Internet comes with AC3 (Dolby Digital) audio. This is great for people that have Media Center PCs or 6-speaker hookups on their computer. But it's an Olympic-sized pain for those of us that have portable players or set-top DVD players that will play back XviD or DivX video with MP3 audio only. My Archos player, for example, will play DivX and Xvid videos; with MP3 sound, the movie file plays correctly; with AC3 audio, the video portion plays, but the audio is completely silent (since the Archos player can't decode AC3).

If you're like me and are stuck in MP3land, there aren't a lot of "one-click" options to convert the audio from AC3 to MP3. Fortunately, by going through the back door of one of the most popular freeware conversion programs, this process can be done with just a few mouse clicks and a few minutes time.

To re-encode an AVI file from AC3 to MP3 you will need the following:

Summary:

We will use the version of VirtualDub that comes with AutoGK to convert the audio portion of an AVI file from AC to MP3.

Why?

AVI files are somewhat unique in that there's no single AVI "format". Instead, AVI is a "container" format in that the files usually include a video portion and an audio portion. The video portion can be encoded in any number of formats, although XviD and DivX are the most popular. The audio portion is usually encoded in AC3 or MP3 format (although theoretically there's nothing to stop someone from encoding the audio in AAC, OGG, FLAC or WAV format). These audio and video portions can be matched in any number of ways: XviD video with AC3 audio, XviD video with MP3 audio, DivX with AC3 audio, DivX with MP3 audio, and so on. You can even have an AVI file with multiple audio tracks, such as a multiple language soundtracks, or a film with AC3 audio for the movie and MP3 audio for the "director's commentary"!

You could always re-encode the video using AutoGK or Super, but this is usually not a viable option. Re-encoding takes at least an hour (typically an hour and a half or two hours on my P4 system). It can also produce less than stellar results, especially with the options available in these "all-in-one" type programs. They're designed to be as user-friendly as possible, and trying to re-encode only the audio portion is not possible in the GUI. And even if these programs *did* work without fail, it'd still be silly: an AVI file is simply two long video and audio files in a single container. Why repaint the entire house when all you really want to do is repaint the shed out back?

Assumptions

This "how-to" article assumes that you are trying to convert to MP3 a video that has a single AC3 soundtrack. Converting movies with mutiple audio tracks is slightly more difficult and will not be covered in this article.

Step By Step:

1) If you don't have it on your system already, download and install AutoGK. Note the AutoGK isn't really a "program" per se, but is actually what's called a "front end", which in this context means "something that looks like a program, but is actually only storing a bunch of commands that it will issue to other programs". What this means is that the AutoGK setup will spawn three or four "setup routines" for things like VirtualDubMod, AVISynth and the XviD codec. This is completely normal. These programs are completely harmless, so just click "OK" and "Finish" when needed to complete the setup process.

2) Once AutoGK setup is complete, open My Computer or Windows Explorer and navigate to the folder you just installed AutoGK into (by default, this is in C:\Program Files\AutoGK, although you might have opted to install it in a different location). Once there, open the "VDubMod" folder and see if there's a file inside called "VirtualDubMod.exe". If so, skip to the next step. If not, keep looking for the file.

3) Double-click on VirtualDubMod.exe. You should see a window that looks like this:

7) Right-click on the AVI file listed and choose "Full Processing Mode". Then right-click again and choose "Compression". A window should pop-up that looks something like this:

11) You will see a new window that looks like this:

Contrary to the progress indicator (above), conversion should take only around 10-15 minutes on a modern computer. Once the progress box disappears, the file is done!

Relax, man... it happens. If you follow the steps above and get a video that looks and sounds pretty good but is out of sync, follow these steps to fix it:

1) Download and install VLC, a video player (and really, you should be using VLC anyway - it's easily the best video player for the Windows platform).

2) Open the out-of sync file using VLC and verify that it's still out of sync.

3) Press the STOP button in VLC and then click on Settings > Preferences.

4) You will see a screen that looks like this:

7) Open VirtualDub again and repeat steps 4-8 in the original instructions but DO NOT exit out of the "Available streams" screen yet.

8) Right-click on the AVI file and choose "Interleaving". In the "Audio skew correction" box, enter the number you entered in VLC into the box, then click OK: