DGMPGDec Quick Start Guide

This document is intended to help newcomers to DGMPGDec to quickly understand the process and become productive. It is intentionally short and to the point, and is not intended to be a complete users manual or tutorial.

What is DGMPGDec?

DGMPGDec is an MPEG decoder suite. It is used to decode MPEG1 or MPEG2 streams from such sources as DVD VOBs, captured transport streams, *.mpg/*.m2v/*.pva files, etc. Perhaps its most common use is in decoding VOBs from DVDs.

What Do I Need to Use It?

You need the DGMPGDec package and Avisynth. First get Avisynth 2.5 (or better) and install it:

Avisynth 2.5

You are going to use DGIndex.exe and DGDecode.dll from the DGMPGDec package, so extract them from the ZIP file and put them together in a directory.

Also get VirtualDub as we will use that to view the decoded video:

VirtualDub Web Site

We'll assume you have a VOB that you have obtained from a DVD (possibly using Smart Ripper, or other such tool).

OK. Now What?

Fire up DGIndex. Using File/Open, open your VOB. You should see the video. Now select Audio/Output Method/Demux All Tracks. That will cause your audio to be saved in a file(s) when you save the project.

Now select File/Save Project and enter a name for the index file (D2V file) that is going to be generated. Suppose your VOB is called 'myvob.vob'; you might choose the name 'myvob' to enter here, because DGIndex will automatically append '.d2v'. Good. Hit Save. The indexing process will start and you'll see the indicator moving along the time line to indicate the progress. Be patient if your video is large. When the process finishes, exit DGIndex.

What is This Index File and What Do I Do with It?

DGIndex created an index file called *.d2v. It is read by DGDecode, which actually decodes the MPEG and delivers the video. The index file just contains information that tells DGDecode where each frame is located and some information about each frame.

But you can't just execute DGDecode directly! It has to be done through Avisynth. We'll make a script file called myvob.avs using a text editor. Later in this document I'll show you how to configure DGIndex to make the script automatically, but for now, you need to know the old-fashioned way. So put this text into a new text file you make called 'myvob.avs':


Replace the path '...' in the first line with the path to the location where you placed DGDecode.dll.

Finally, use VirtualDub to open the 'myvob.avs' script file just as if it was an AVI file. That's it! You have your video and can navigate randomly on the VirtualDub timeline. Does life get much sweeter than this?

Sure, Sure, But What About My Audio

DGIndex saved your audio in a file(s). It will have a ".wav", ".ac3", or ".mpa" extension. If you have a ".wav" file, you can load that directly in VirtualDub. But you can also use Avisynth, which gives you access to powerful audio filtering.

Suppose we have a ".wav" file. Our Avisynth script will be like this:


Now when you open this script in VirtualDub, you will have video and audio.

We saw processing for a ".wav" audio file above. You need the corresponding source filter for the type of audio you have. Use WAVSource() for ".wav", MPASource() for ".mpa", AC3Source() for ".ac3", etc. WAVSource() is built into Avisynth. The others can be found here: Avisynth Filter Collection.

Don't forget to use LoadPlugin() to load your audio source filter. And read the Avisynth documentation to learn about how to adjust the audio/video synchronization using DelayAudio(), and other useful things.

Yeah, But How Do I Do That Automatic Script File Thing?

Ahh, you have to pay extra for that! No, not really.

Let's suppose you have a script that you use all the time. Maybe like this:


Copy this to a file and call it 'template.avs'. Then edit it to replace the D2V file name with __vid__ (that's two underscores before "vid" and two after). template.avs should then look like this:


You see, DGIndex is going to use this as a template and insert the right file name whenever it sees __vid__. Slick, eh? You can also use __aud__ to generate the audio filename; refer to the DGIndex users manual for details.

OK, all you have to do now is fire up DGIndex, select your template file with the Options/AVS Template menu item, and then do a Save Project. If the *.avs file does not already exist, DGIndex will make one for you based on the template! Of course, the template has to be created only once, while you'll get an automatically generated AVS script every time you save a DGIndex project.

Cool. One Last Question...


Why the Two-Step Tango? Why Can't I Do Everything Right in DGIndex?

Good question! We want to make our video available to any application that we might find useful. Surely we can't put every possible function into DGIndex. So instead we create a way to 'serve' the video into all these other applications. Avisynth is an AVI file server. It creates a 'fake AVI' and tricks applications into thinking they have a real AVI when they open the *.avs file.

If you just want to make an AVI out of your video, it's easy. Open the AVS in VirtualDub, set your compression, and do Save AVI.

There's another way to serve called 'VFAPI' that is also supported, but you get the idea: we are just setting up serving of the decoded MPEG2 video with DGMPGDec. The receiving application then does its thing without even knowing it has been tricked.

Copyright (C) 2004, 2005 Donald A. Graft, All Rights Reserved