.AC3 Quality vs .MP2, and Why Does .MP2 Not Always Play?

[Equus]

Hi again,

A couple questions about audio. Someone told me that .AC3 audio is actually not as good as .MP2 (PCM) audio because it's so compressed but .AC3 is the only one of the two that will do surround sound. Any comments on that?

Also, I'm having trouble getting the audio from DVD's I author with Sizzle or FFmpegX to play audio when I've encoded in .MP2. This is because I have the audio out on my set-top Toshiba to "bitstream" to go out through the optical out. If I change it to "PCM" out, then I can hear the audio, but I don't want to have to do that every time, and I've noticed that when I burn a DVD in iDVD, the audio plays just fine, even though iDVD encodes using PCM Audio (.MP2 I presume) not Dolby Digital (.AC3).

Any ideas about this? I'm tired of having to re-encode the audio from the original .aiff file into .AC3 using DVDSP's A.Pack, cuz it takes as long as the real-time of the file.

Thanks,

Eq

[brett]

a couple things that may or may not help you: .mp2 is not .pcm; .mp2 is compressed, .pcm is not; .pcm is raw audio like .wav or .aif; .mp2 is not dvd spec, and thus not all dvd players support it; idvd encodes audio with .pcm.

i'm sure someone else has more info tailored to your situation.

[sterno]

Like brett said, MP2 is not PCM - MP2 is MPEG-1 Layer-2 audio compression, PCM is uncompressed digital stereo. AC3 is another compressed format, which allows multichannel sound (surround). PCM is higher quality than AC3 or MP2 because it's uncompressed and both MP2 and AC3 are lossy compression. However, you probably won't be able to hear the difference as long as your bitrate is high enough on the compressed formats, and the uncompressed PCM audio is very, very large.

At a guess, the reason you have trouble with the MP2 audio is that it's not an officially-supported audio format for NTSC DVDs. I think it is officially supported on PAL, so if you're in the PAL world it may just be a compatibility thing with your player - I think MP2 audio is pretty rare. iDVD is giving you uncompressed PCM, which is supported on both NTSC and PAL.

[Equus]

Wow! I didn't know that about PCM. I thought .MP2 was PCM but now I see it's another form of compression. I'm on NTSC, and my DVD player will play the audio on a DVD I author with .mp2, but I have to manually switch the audio setting on the player from "bitstream" to "PCM". That's kinda strange since .mp2 isn't PCM. Weird.

Anyhow, so is there any other way to author my DVD's with true PCM like iDVD does? Because iDVD doesn't allow for more than 90 minutes. I've been encoding with the Quicktime Pro MPEG-2 Encoder then authoring with Sizzle, but I have to have Quicktime Pro save the audio as AIFF, then encode that to .ac3 with A. Pack, which adds about 1-2 hours to the process. If I'm working with a file like a VHS recording that doesn't have surround sound to begin with, I'd rather just go straight to uncompressed audio, if that were possible and size allows for it.

Thanks,

Eq

[ZeroSix]

when you are exporting using Quicktime, you know how you end up with a .aif file? Thats the PCM you are looking for. Drop it onto DVDSP or mux it with your .m2v file and you are all set.

AIF = PCM audio. PCM is generally not any specific format [except the newer .pcm file type], just a term for uncompressed digital audio.

[Thargok]

MP2 audio is supported by the DVD spec (or rather the ifo spec). This spec is for both nstc and pal. If the dvd isn't working, you authored it wrong.

[Equus]

Zero-Six, you are a font of knowledge! However, I can't seem to get any of the authoring programs except DVDSP to accept the .aif file for muxing. I haven't learned DVDSP yet (haven't opened the manual yet...too intimidating!). Neither Sizzle or FFmpegX seem to accept an .aif audio file. Do you have any ideas about that?

Also, do you know why Quicktime Pro doesn't give me the option of exporting and .mp2 file into .aif? Usually that option is there but not when I have an .mp2 file open. I can do it in iTunes, strangely enough!

Thargok, as I said earlier, my DVD player WILL play .mp2, but I have to change the audio output setting on the player from Bitstream to PCM. If you have any idea of a way around this during authoring, please let me know.

Thanks,

Eq

[brett]

yes, even though i use .mp2 all the time for my dvds, i did not know it was dvd spec -- my bad.

http://www.dvddemystified.com/dvdfaq.html#3.6

i didn't know it could do 5.1 & 7.1. hmm.

[Equus]

So why then does my DVD player require me to manually change the output from "Bitstream" to "PCM" to hear the audio on a DVD encoded with .mp2 when

a).mp2 is not PCM and
b) iDVD's PCM DVD's play just fine when set to bitstream.

Weird

[orygun]

I too can't get Sizzle or FFMPEG to accept AIFF files that are exported from Quicktime. Anyone know how?

[Equus]

Per Henry (Sizzle's creator): Sizzle does not accept AIFF files. Nor does FFmpegx. The only way I can see to do it is with DVD Studio Pro.

Eq

[ZeroSix]

riiiight.... sorry for not being clearer about the .aif format.

If you want to use any other tool besides DVDSP, just open the .aif into Quicktime and export it to a .wav file. You will experience zero loss in quality if you set the export settings to match your source file.

The reason you cann edit MP2 files in Quicktime is because they are MPEG based. it is the same reason you cannot do much with MP3s, which are ALSO MPEG based. the use of iTunes works well for converting MP2 files, although the interface is bulky.

:/

[Equus]

Zero-Six:

You continue to amaze me! The .wav works great for FFmpegX. Sizzle will of course still only take .mp2 or .ac3.

Quick question: do you have any idea why DVDSP won't take a graphic that has been saved as a .psd (Photoshop) file in Preview or Graphic Converter for one of its menu assets? Do I have to go out and buy Photoshop in order to make graphic menus?

Eq

[ZeroSix]

you can either use Photoshop made PSD files OR you can use Corel to make layered PICT files. Either should work fine.

No Mac user should be without Photoshop anyway.

Out of curiousity, what is the error message you are getting when trying to import Non-Photoshop made PSD files?

[Equus]

Zero-Six:

Your continued assistance is appreciated. I'm not getting an error, but the non-photoshop .psd files are grayed-out in the browser window when I go to import them, ie. I can't select them.

I might get PhotoShop elements, or else just use moving menus in m2v format if I decide to use DVDSP for my authoring.

Very Important: Could you see my message in the Authoring/Resolution Problems Topic? I'm not getting success with Toast 6.

Thanks,

Eq