audio extract WITH compression

[macyman]

I have extracted audio as usual with VirtualDub but
for some strange reason it is much bigger than
original avi file (like 400 MB more). When encoding
this of course causes me to create a much larger
mpeg and thus will not fit on 1 CD.
Now, my question is: is it a MUST to extract audio
uncompressed? Couldn't I extract with some kind of
compression so at least I get a normal sized audio .wav file?
Thanks!

[deramon]

I assume you extracted the wav to be able to re-encode to mpg format. So the size of the wav file will not have anything to do with the size of the final mpg.

[DJRumpy]

You should also know that WAV is not exactly compressed anyway. You could convert directly from one format to another, but almost all converters use a temporary file, which is still a wav file during the conversion. Save yourself the grief.

Even a full uncompressed wav file for an entire movie is pretty small compared to the companion video. I suppose you could try changing the audio compression settings in Virtual Dub, and set it for full processing mode. Optionally, just leave your audio where it's at, and specify the original AVI as your audio source in virtual dub. I've never tried that, as storage is cheap. Who cares about anything less than a gig?

[PigOnWing]

A few misconceptions:

I have extracted audio as usual with VirtualDub but for some strange reason it is much bigger than original avi file (like 400 MB more). When encoding this of course causes me to create a much larger mpeg

1. When you mean 'as usual', do you, by any chance, mean 'using Full Processing mode' on the 'Audio' menu?
2. Regardless of the answer, and regardless of the resulting file, this most certainly does not 'of course' means it will produce a larger MPEG.

You should also know that WAV is not exactly compressed anyway.

Not entirely true. Uncompressed WAV, aka RAW wav, is (surprise surprise) uncompressed.
But pretty much any (most?) audio compression formats can have a 'WAV header'. If you have a DivX video for example, with the audio being encoded in MP3/DivX Audio/Windows Media V2/Whatever, and extracting the WAV using 'Direct Stream Copy', you'll get a WAV file which is, infact, compressed (Which answers the original question - yes, you can, however - read further on).


While I would indeed recommend to use the 'Full Processing Mode' to extract a truly uncompressed WAV from VDub - if you must use a WAV (a better way would be to transcode the audio directly from one format to another, using BeSweet, for example) - the final audio size is determined by one and only one factor: the bitrate allocated for it.

If you're allocating 224Kbps for the audio stream, in your final encode, then the audio will occupy 224Kbit times length of movie in seconds.

Lowering the audio bitrate will lower the filesize, however I doubt that the difference will be more than negligible. Lowering the video bitrate might make more of a difference (but of course, lower either will affect the quality of either, respectively).

-- Piggie

[DJRumpy]

Sorry Piggie, I mispoke myself. I meant a PCM wav (uncompressed), which I think is the default for VirtualDub, when selecting FILE | SAVE AS WAVE, with full processing OFF.

[PigOnWing]

Full Processing Off = Direct Stream Copy = No change in the audio stream.
If the original is compressed, the compression will be directly streamed to the resulting WAV.

-- Piggie

[DJRumpy]

(*DOH!*) I know that. Don't know where my head is. I use it all the time to extract AC3 from DIVX files.

I'm going to shoot myself in the head. I'll be back later.