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
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
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.
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!
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