ac-3 is 5.1 channels right? can mp3 support that many channels as well?

[Noriaki]

ac-3 is 5.1 channels right? can mp3 support that many channels as well?

A friend is wondering why the AC-3 audio stream is 400MB and his high quality mp3 stream is only 100MB.

They are both compressed....I'm thinking it's mainly because the AC-3 stream is 5.1 channels and the mp3 is 2 channels. Is that right, or is there some other reason?

 

[Oscar1613]

mp3 is stereo... AAC can have multiple channels and gets smaller files for equal bitrates as mp3's in stereo files... not sure how it compares to AC-3 with multichannel files tho...

 

[Ameesh]

no 5.1 is ac-3, mp3 does not support 5.1 channell encoding

the windows media codec "corona" supports up to 8.1 i believe.

its small and higher quality then mp3.

 

[tweakmm]

The mp3 stream is still probably compressed more

 

[conjur]

AC-3 is just Dolby Digital. It typically is 5.1 but it could even be mono or just 2.0. It just means it's digital.

 

[StattlichPassat]

Originally posted by: conjur
AC-3 is just Dolby Digital. It typically is 5.1 but it could even be mono or just 2.0. It just means it's digital.

Ahhhh...

 

[HendrixFan]

AC3 is the file extension for Dolby Digital sound files. It is a compression format, much like MP3, just a different codec. DTS is another compression method.

AC3 files can range from 1.0 to 5.1. Most newer movies compress the audio at 448k/s, which is around 90k per channel, roughly equal to a 192k MP3 (in stereo - 2 channels). Personally, Ive seen nothing that shows me that Dolby Digital encoding is any better, by bitrate, than a LAME encoded MP3. But MP3 files can only support 1.0 or 2.0 (mono or stereo).

AAC is a new compression format, supposed to be based of MPEG4, but never seems to get past liscensing issues. It can support up to 32 channels if I remember correctly. It is supposed to offer better compression than MP3, but I know the difference cant be tremendous, the only advantage then would be the multichannel support.

 

[Noriaki]

Originally posted by: conjur
AC-3 is just Dolby Digital. It typically is 5.1 but it could even be mono or just 2.0. It just means it's digital.

Oh yeah...AC-3 doesn't have to be 5.1 channel.

We're just looking for a reason why the MP3 is 1/4 the size of the AC-3 stream (this is for a DivX to VCD conversion BTW).

I'm thinking that the AC-3 stream was 5.1 channel, and the MP3 doesn't maintain that, and that's why it's so much smaller.

And yeah the MP3 would still be compressed more. 5.1 -> 2 is less than a 1/4 reduction. But AC-3 is compressed, and it doesn't seem likely that is 4x less effecient than MP3...

 

[HendrixFan]

Like I said, most 5.1 DD AC3 files are 448k/sec. That is roughly equivalent to a 192k MP3. Most DivX movies you get dont use high audio bitrates like 192k. Frankly most movies dont need it. THere is alot of silence and alot of dialogue. A VBR MP3 should come out around 120-140k average, because most scenes wont use much bitrate. IF the AC3 format supported VBR, you could get better size/quality ratio. DVD's MPEG2 video mostly use VBR, its a wonder why the audio doesnt.

Most divx movies I download use 96k MP3 (or WMA ugghh!), which is too low for my tastes. Most DivX's I make for myself use VBR MP3s, at the bitrate I mentioned above. That is likely why its 4 times the filesize.

 

[Noriaki]

I didn't read your last post before I wrote mine

Thanks for the info though, yeah he is using a VBR MP3 for his audio stream.

So I guess that's why it's so much smaller

Thanks for the info.

 

[NuclearFusi0n]

all my divx rips use the original AC3 soundtrack

 

[HendrixFan]

If filesize is an issue, you can always re-encode the AC3 at a lower bitrate as well. With Soft Encode, you can encode at 384k, which a few 5.1 DVDs use. Or you can do it at 320k, and encode it at 4.0. The center channel will get put on the L an R equally, creating a "phantom" center, and the LFE channel will be put in the front speakers.

Personally, I dont think most movies are worth having 5.1, the surround channels just arent used but for a few occasions. LOTR or Star Wars are a couple movies that make really good use of all the channels. Its all up to your own tastes of course.

 

[Maverick]

Originally posted by: Ameesh
no 5.1 is ac-3, mp3 does not support 5.1 channell encoding

the windows media codec "corona" supports up to 8.1 i believe.

its small and higher quality then mp3.

what do you work for microsoft or something?

is this corona thing out yet?

 

[HendrixFan]

MS is heavily promoting WMP9 which includes surround sound audio (WMA) and HDTV resolution video (WMV) support. Personally, I would avoid using a codec that requires an MS OS, muchless their codec which is likely to be restricted to use with WMP and soon-to-be DRM.

 

[Mrburns2007]

Dobly Digital is great for movies but not very good for high definition music. There is a DVD-audio which is pretty good but not very popular because you really need a high end audio system to get results.

 

[Lithium381]

i thought that mp3 was just a new compression method.....so technically can't you create a 5.1 file format that's compressed to mp3.......as opposed to straight up pcm?

 

[OneOfTheseDays]

you'll find a good share of divx movies on the net these days with the orignial AC3 sound instead of compressed mp3 sound.

 

[Lithium381]

i ALWAYS encode my divx's to use VBR mp3's.........saves space i use for video