VBR audio

[pentaX]

Hi, is there any tool that shows the max bitrate of the VBR audio in a AVI file?
The matter is that I want to convert it to an AC3 2ch file (with ac3machine) and I don't know what bitrate choose to encode? I guess that if I choose the average bitrate that shows many programs I'll lose audio quality.
Any solution?
Thx

[pacohaas]

no matter what, you're going to lose quality simply because you are re-encoding. If you want to preserve as much quality as possible, use the highest bitrate AC3 that you can, regardless of the average or max bitrate of the mp3.

But to answer your question, if you demux the mp3 with virtualdub or something, then you should be able to see the max bitrate(amongst many other things).

[bond]

btw. why do you want to transcode to ac3?

[pentaX]

i wanna make a dvd from a divx .avi file with VBR mp3 audio, so i have to convert the mp3 to ac3 or mp2 to drag it into dvdmaestro.

btw, if i check the avi with gspot tool it says:
"114 kb/s (57/ch, stereo) VBR LAME3.89"
but that's the average bitrate, i suppose. I guess there will be parts where the bitrate goes above that, right?

on the other hand, if i open the avi with virtualdub it advices me to decompress to WAV and recompress it with CBR 113.7 +- 9 kbps.

does this means that is the sound will be the same converting it to 128 kbps and converting it to 320 kbps ???

[Fr4nz]

Imagine this: Take a VHS. You make a copy of this VHS. Then you take the copy and make a copy of the copy. Obviously there will be a quality degradation.

This happens also when you reencode a compressed song. Every time you encode a track/song you will lost some of the original infos because of the encoder psychoacoustic model which throws away parts of the sound that thinks it is inaudible for human ears.

The more bitrate is high, the more the original sound is "preserved".

[pacohaas]

Originally posted by pentaX
does this means that is the sound will be the same converting it to 128 kbps and converting it to 320 kbps ??? no, doing this will degrade the quality twice:

1 - when encoding to CBR 128
2 - when converting it to CBR 320 (yes, the CBR 320 will be worse than the CBR 128 because every re-encode, regardless of bitrate, will lose quality, this is what it means to be a lossy compressor)

so, try to keep the re-encodes to a minimum.

[pentaX]

no i didn't meant that (sorry my english is not very good)

i mean, will it be the same quality if i convert it to 128 kbps or to the max possible quality?

In conclusion, what bitrate do you advice to choose for the CBR from the following options:

* gspot: 114 kb/s (57/ch, stereo) VBR LAME3.89
* vdub: decompress to WAV and recompress it with CBR 113.7 +- 9 kbps
* demuxing the avi to .mp3 with virtualdubmod and selecting properties of the mp3 in windows explorer shows 283 kbps.

What program do i have to believe?

[r0cket]

gspot and vdub shows right bitrate, windows' explorer can't deal with bitrate of vbr mp3.
and like Fr4nz said, the higher the bitrate, the safer is transcoding. you'll get the best result if you'll use the highest bitrate possible with ac3 (well, if it is stereo, imo going above 256 would be overrun).