DivX Audio Multiplexing with VirtualDub

To multiplex is to merge (interleave) an audio file with a video file. All our AVI multiplexing is done with VirtualDub. VirtualDub is the most useful and powerful video editing application you will ever download! It is more useful than other video editing applications that would cost hundreds of pounds to buy - it is also the easiest of them to learn! And what's more, its free! For more details on using this amazing application check out my Advanced VirtualDub section.

Whatever method you used to extract your audio to PCM Wav the method for multiplexing is the same. Open your movie file in VirtualDub by going to File > Open video file...

We don't want to effect the video itself so we use Video > Direct stream copy. Whenever we select an option, VirtualDub adds a black dot by it to tell us it is selected.

Then select Audio > Full processing mode.

SELECT THE WAVE

If you used PCM audio in Flask Mpeg to create the audio for your AVI then you can skip this bit and move on to 'Converting the Samplerate'. Flask mixes the PCM audio with the video, so all we would need to do is compress the audio. But for those who exracted the audio with Graphedit or Ac3Dec or Normalized the audio seperately, we select it like this:

Choose Audio > WAV Audio.

When we do this VirtualDub will ask us to locate the wave file we wish to use. Do so and select Open.

CONVERTING THE SAMPLERATE

If your audio file was sampled at 48,000Hz, as is usually the case with DVD audio, then it is better we convert it to 44,100Hz. For more details on this subject read my article called "Fixing Bad Audio".

Choose Audio > Conversion...

Choose 44100Hz and make sure the 'High quality' is selected, and press OK.

COMPRESSING THE AUDIO

Finally, because a PCM wave file for the average movie is something like 1 to 2 gigabytes in size, we will need to compress it to MP3 or WMA audio. To do this choose Audio > Compression...

Choose MPEG Layer-3. Hit the 'show all formats box' and then select 96kBit/s, 44100Hz, Stereo. If you want even higher quality audio (i.e. perhaps this is a music video), then you can choose 128 kBits/s 44100Hz stereo. This is said to be equivalent to CD quality audio! On the other hand, if you really want loads more audio compression, you can choose radio quality 64 kBit/s 44100Hz mono.

Alternatively you can use WMA audio (which is called Divx Audio because it comes hacked with the DivX codec). Choose DivX ;-) Audio. Then choose 64 kbps, 44 kHz, stereo for Divx ;-). This is the most reliable WMA format that keeps best synching.

WMA audio compresses about 5 times faster than MP3 and the quality is slightly better at lower bitrates! Nevertheless, MP3 at 96 kBit/s is superior quality to 64 kbps WMA audio, so the choice is yours. One final warning about WMA audio. It doesn't always keep perfect timing. For example, if the move is long, then it may end up a quarter of a second or so shorter than the video length. I find this easy to correct by using my synching techniques. But if you want to more or less guarantee a perfect synch, then choose MP3.

PROCESS IT

Okay, all we need to do is select the Save AVI... option to save our final movie =)

Up will pop the progress box. You can uncheck the show 'input' and 'output' video options to speed it up a bit. You can also choose a higher priority setting to help VirtualDub do the job faster by hogging more CPU power.

That's it! In less than 3 hours you should have perfect audio with your DivX video!