Audio re-compression

[VRYK]

An XVID file loaded into VirtualDub posts the warning message: “AVI : Variable bitrate (VBR) audio detected. VBR audio in audio is non-standard ….Preferences, AVI bitrate 102.8 ± 11.6 kbps”.

Normally I use MPEG Layer 3 for audio re-compression, but in the present case the maximum rate shown in the Select audio compression window is 56 kbps for this mode.

I would be grateful for help on which compression to use.

[paglamon]

Install Lame ACM MP3 codec. Now open Virtualdub and under Audio compression you will find Lame mp3.Select it ,and you will find more bitrates available.

[VRYK]

Many thanks for your reply.

I have installed the Lame ACM MP3. I plan on using the 100 kbps bitrate since the next one up is 128 kbps. Can the other parameters in the Select audio compression window be ignored when making this choice ?

Best wishes

[paglamon]

since the next one up is 128 kbps

Nope. There are more options between 100 and 128. You just have to select "Show all formats".

[VRYK]

Many thanks for your reply.

I am at a loss regarding the other parameters in the compression window. Should I opt for a constant bit rate (CBR) or variable (both are available at 112 kbps) ?

Best wishes.

[UncasMS]

I'd give it a first try and leave the audio stream UNTOUCHED - ignore this warning and go ahead.

[paglamon]

Should I opt for a constant bit rate (CBR) or variable (both are available at 112 kbps) ?

Ofcourse VBR is theoretically better. But then , Virtualdub has problems with VBR audio. This is one reason why I often prefer AVIDemux over Virtualdub.
And as UncasMS suggested, why not forget about recompressing the audio and make a direct stream copy of it and see what happens?

[VRYK]

Many thanks for your reply.

Since the warning is conditional I have wondered about how seriously to take it, but have always recompressed with a view to not wasting CDs.

I guess it boils down to being an empirical question.

Best wishes.

[VRYK]

Many thanks for your reply.

Would I be right in thinking that VBR is to audio what 2-pass compression is to video ?

Best wishes.

[paglamon]

No. VBR is same in audio as in video. That is,it uses variable bitrates while encoding different parts of the audio or video. Suppose a part of audio is relatively silent.If VBR is chosen,the encoder might use less bitrate to encode that part and use a higher bitrate for a more noisy part.