[vorbis] AVI stream w/ AC3 5.1ch

[Paul E]

smoerk wrote:

> Christopher Granade wrote:
>
>> Perhaps I misunderstand what AC3 is... I did not think it was
>> compressed. The problem is, that out of a 900MB file, 150-160 of that is
>> audio. Once again, thanks for the help! (/me goes to doom9 forums as
>> suggested...)
>
> what's wrong with this, it's around 17% of the bandwith for the audio 
> signal. i would it's a maximum of 256 kbps for a 5.1 signal, which is 
> not too much, you should be able to hear the ac3 compression. i doubt 
> you can get much lower with vorbis without getting much worse audio 
> quality (you are lossly compressing a already lossly compressed signal). 

I ran some tests myself.  I ripped the AC3 tracks for My Big Fat Greek 
Wedding and Matrix from my DVDs.  I then encoded them at quality zero to 
Vorbis.  I chose Matrix because it makes extensive use of the surround 
sound and My Big Fat Greek Wedding is a more average example of 5.1 AC3 
usage.  For Matrix the Vorbis file was 58% smaller and for My Big Fat 
Greek Wedding it was 69% smaller.  Those are large numbers.  And the 
sound was still fine.  Quality zero for 6 channels (since Vorbis 
doesn't, at least right now, have a .1 channel) was reported as being 
288 kbps nominal bitrate.  But most of the time it was well below 130 
kbps.  In fact Matrix averaged 162 kbps and My Big Fat Greek Wedding 
averaged in at 121 kbps.  That's 5.1 surround at or below bitrates most 
people use for stereo mp3 files, and to me Q0 in Vorbis (which is what I 
encode my library of music in) sounds much, much, better than 128kbit 
mp3 or even 192kbit mp3.

Paul

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