Difference between AC3 and MPEG 2ch audio

[gf]

Greetings,
I have a stupid question, I am backing up a disc and it has on some files AC3 and MPEG 2 ch audio, on other files it has AC3. My dvd player (Pioneer dv434) has no AC3 decoder but plays the dvd end to end with no audio loss, could I drop the MPEG2 audio (for some needed disc space)?
Thanks
Steve

[daamon]

Hi gf,

I'm a bit confused about what you've got and what you're wanting to do.

But, if I tell you that the AC3 audio format is a standard for both NTSC and PAL DVD's and that all stand-alone DVD players should accept it and play it, then hopefully that will help you...

[indolikaa]

Keep the AC3 streams.

(MP2 is not a DVD-legal audio stream in the NTSC world, and there's talk of it becoming non-legal in the PAL world as well.)

[bugster]

(MP2 is not a DVD-legal audio stream in the NTSC world, and there's talk of it becoming non-legal in the PAL world as well.)

Change the "DVD-legal" to "mandatory to support" or something similiar and I will agree with you.

DTS is not mandatory on DVD's, but is widely supported and advertised.

[gf]

I am trying to back up the (2) disc Led Zepplin disc with dvd shrink, and the data rate seems a little too low, slight macroblocks, and I wanted to remove more "stuff" so the video data rate would increase (less shrinkage). I try the info tonight.
Thanks
Steve

[SLK001]

Change the "DVD-legal" to "mandatory to support" or something similiar and I will agree with you.

DTS is not mandatory on DVD's, but is widely supported and advertised.

How about "MP2 audio is not part of the NTSC spec". And, DTS is part of the NTSC spec (under Private Streams), so it is supported.

And, gf, your player DOES have an .AC3 decoder (in fact, all of them do). It just doesn't have the multichannel (i.e., 5.1) outputs. It just mixes the multichannel stuff to L/R channels only.

[bugster]

Change the "DVD-legal" to "mandatory to support" or something similiar and I will agree with you.

DTS is not mandatory on DVD's, but is widely supported and advertised.

How about "MP2 audio is not part of the NTSC spec". And, DTS is part of the NTSC spec (under Private Streams), so it is supported.

.

Thats fine, I was just being pedantic.

[indolikaa]

How about this?

"Use PCM audio streams only, you tight-wad, bit-crunching bastards! Quit being nonconformists !"

[RabidDog]

Addendum : which is smaller mp2 audio @ say 192 or ac3 2ch @192 ?? How much bigger is the full surround sound Ac3 than the simple 2ch Ac3? (of the same soundtrack).

[SaSi]

Addendum : which is smaller mp2 audio @ say 192 or ac3 2ch @192 ?? How much bigger is the full surround sound Ac3 than the simple 2ch Ac3? (of the same soundtrack).

Any codec format at the same bitrate produce identical size streams.

A full surround sound (5.1) will not be encoded at 192kbps because each of the 6 channels will be starved for bitrate. Typically it takes ~480kbps.

If you are really pressed for space, one thing to do would be to re-encode the audio into 2 channel something. I personally favour MPEG layer 2 at 192kbps or even less if the movie doesn't have too many audio effects. This, of course, if I really need to reduce the audio track size. And since I don't have a 5.1 audio system and don't really intend to get one, I don't really care about the 6 channels.

But then again, if you have 6 speakers and you want to compress a really long movie with a "fat" soundtrack, perhaps the best approach would be to demux the movie into an AC3 5.1 audio track and the MPEG-2 video track, leave the audio alone and re-encode the video with a descent MPEG encoder. Tmpgenc will do wonders with 2 pass enoding, but take time in the order of 10 ~ 12 hours (thinking of a 3 hour movie and a P4/2GHz).

Re-encoding the movie will typically produce much better results compared with any DVDShrink, DVD2One or other transcoders.

[RabidDog]

I also dont have a 5.1 speakers. What I really meant is which preserves more detail for the same filesize.. I suspect it should be ac3 as thats more modern (2.0 ac3 vs 2.0 mp2, stereo).

[SaSi]

I also dont have a 5.1 speakers. What I really meant is which preserves more detail for the same filesize.. I suspect it should be ac3 as thats more modern (2.0 ac3 vs 2.0 mp2, stereo).

In that you are correct. AC3 is better than MPEG 1 Layer II. Probably equal in quality when AC3 is 128 and MP2 is 192.

[RabidDog]

Now for the difficult question ..For the same filesize which will sound better/preserve more detail (all stereo) mp3 @128 or AC3@128. anybody? I suppose the best way to test this would be with an orchestral track..

[tsantsa]

Good question RabidDog. I myself am wrestling with reencoding some music from mp2 audio to ac3. I was wondering what bit rates I can use to equal the same quality without choking the sound.

I was wondering if anyone has a link to side by side comparisons of ac3>mp2>lpcm at various bitrates.

[vcdforme]

I've been experimenting a bit.
I'm a bit of a bit-crunching bastard, trying to squeeze in as much
video as possible. But I do care about good sound....
I've settled in with 192k bitrates. Sounds quite good to me.
Between AC3 and Mpeg, if I recall, the AC3 file seems to be
about 20 percent smaller in size. I can't say one is better than the
other, they both sound good. I'll just use AC3 if I'm really pressed
for space. Even though the AC3 should be more "compatible", it
doesn't seem to make much difference between my 4 players.
Media seems to have more to do on that....

I use soft-encode for AC3 but find it cumbersome. I'd buy the DVDAUTHOR-AC3 module in a heartbeat if I didn't have to hook
up to the net to verify the damn copyprotection. I don't connect
my work machines to the net......sorry that's another story.


Yes, let's see some more AC3 testing!!!

[RabidDog]

Can you consider 684kb Ac3 music as good as lossless, within the bounds of normal human hearing??

[Cannonball888]

Greetings,
I have a stupid question, I am backing up a disc and it has on some files AC3 and MPEG 2 ch audio, on other files it has AC3. My dvd player (Pioneer dv434) has no AC3 decoder but plays the dvd end to end with no audio loss, could I drop the MPEG2 audio (for some needed disc space)?
Thanks
Steve

YES

[SaSi]

Good question RabidDog. I myself am wrestling with reencoding some music from mp2 audio to ac3. I was wondering what bit rates I can use to equal the same quality without choking the sound.

I was wondering if anyone has a link to side by side comparisons of ac3>mp2>lpcm at various bitrates.

Some interesting links:

A thorough comparison of various codecs made by EBU
http://www.ebu.ch/trev_283-kozamernik.pdf

A page with useful links to codec comparisons:
http://www.codecreview.com/