Decompressing Audio

[jot2b]

When I opened a full length movie in VirtualDub, I received the following message before I could do anything:

"VBR audio stream detected

VirtualDub has detected an improper VBR audio encoding in the source AVI file and will rewrite the audio header with standard CBR values during processing for better compatibility. This may introduce up to 115509 ms of skew from the video stream. If this is unacceptable, decompress the *entire* audio stream to an uncompressed WAV file and recompress with a constant bitrate encoder. (bitrate: 139.8 ? 35.3 kbps)"

(? equals a nonstandard keyboard symbol)

I proceeded to process a section of the video under settings that worked fine with previous videos I'd encoded. Unfortunately, the audio turned out terribly out of sync with the video. (The audio was perfectly in sync in the source file.)

I'd like to take the suggestion from the error message, but I have no clue where to begin. What is the best (hopefully free) tool for decompressing audio? And what should I know about the "constant bitrate encoder"?

Thank you!

 

[EvilDragon]

I have no program to decompress audio to wav (can't virtualdub do that?), but I can tell you something about variable and constant bitrate:

MP3 - files can either use a variable or a constant bitrate.

This means:
An MP3 encoded at a constant bitrate (e.g. 128 kbit) ALWAYS has the same bitrate - even if the audio information could be much smaller. But also if the audio information would need more space.

An MP3 encoded at a variable bitrate changes the bitrate during the song - if audio information needs less space, the bitrate goes down.
If audio information needs more space, the bitrate goes up.

Not all players support this, though plus the audio stream cannoted be connected with the video stream - which can lead to audio / video unsynchronized.

 

[reeced]

Virtual Dub will strip the sound off for you as a WAV file - just open your video and then "Save as WAV" in the file menu. Once you've done this then you can re-open your video and this time uner "Audio" select "WAV Audio" as the source.

 

[jot2b]

Thanks for all the useful info Evildragon. Variable vs constant bitrates finally makes sense to me now.

reeced, thank you for the tip. I shouldn't have any problems now!