MP2 bitrate on DVD

[zoobie]

There seems to be controversy over the max bitrate for stereo MP2 audio on a DVD. Some have it as 256 while others mention 384kbps. Which is it?

I know it's best to convert PCM directly to AC3 but I've 25 productions and doing it manually isn't gonna happen.
I have an option to convert MP2 to AC3 in my authoring ap.
Do I gain anything from converting 384kbps MP2 to 384kbps AC3?

Thanks

[El Heggunte]

Should be 384kbps for stereo, and according to the Wiki,

MP2: 48 kHz sampling rate, 1 to 7.1 channels, up to 912 kbit/s

but the firmware of many SAPs might disagree

[jman98]

How the hell after 7 years of membership AND 3000+ posts AND having "25 productions" at once do you not ALREADY know the answer to this? I am speechless.

MP2 audio is not and NEVER has been legal for NTSC audio. Some will tell you that it is if you have another audio track that is LPCM or AC3, but they are wrong. MP2 audio is only legal for PAL DVD. I assume you are not making PAL DVDs since your location is Colorado. Someone will no doubt follow and want to endlessly debate whether MP2 audio is valid for NTSC or not. I can tell you that it's not part of the NTSC DVD requirements that NTSC DVD players be able to decode it. THAT is a fact.

Now having said that, MP2 audio on NTSC DVD most likely will work unless you have a player that rigidly enforces the NTSC specifications. Do such players exist? I don't know. So what you gain by converting to AC3 is not quality but potential compatibility. AC3 audio is always valid for DVD - NTSC or PAL.

384 Kbps is the highest bit rate allowed for MPEG-2 layer I audio. AC3 for DVD can go as high as 448 Kbps. However, going LPCM -> MP2 -> AC3 is converting from lossy MP2 to lossy AC3 so I would expect some degradation in the audio, but if you are lucky most consumers would not notice it. I guess you are doing this on the cheap as many professional or prosumer DVD authoring programs can handle LPCM -> AC3 directly for you. Whatever you are using is really cheap AND old if it produces MP2 audio.

[jman98]

As El Heggunte points out, if you can through some miracle find a multichannel MP2 encoder, you can use a higher bitrate, but the odds are nobody can play it back in multichannel audio. I am not aware of any currently made receivers anywhere in the world that are capable of correctly decoding MP2 multichannel audio. Almost all devices will play it in stereo compatibility mode.

[Cornucopia]

Some Phillips receivers, c.2002-2005 didn't advertise it well but did support Multichannel mp2. I was only ever able to encode using the "Hypercube" software, IIRC. Certainly not worth the trouble...

I second what jman98 pointed out (though maybe not as vociferously).

It's ALWAYS worth it to go to AC3 for compatabilty's sake. It USUALLY worth it to go FROM LPCM for quality's sake.

Scott

[aedipuss]

Some Phillips receivers, c.2002-2005 didn't advertise it well but did support Multichannel mp2. I was only ever able to encode using the "Hypercube" software, IIRC. Certainly not worth the trouble...

hehe yes some of the only svcd 5.1 audio players. i used pub_enc.exe to create 5.1 mp2 svcds.

[zoobie]

Yes...I know all that compatibility crap...which is all it is.

I probably should have asked how much I lose per re/trans-encoding MP2 and AC3 audio using the same bitrate.

My "old" & "cheap" software is Sony Vegas Pro 10c but without DVDA. This cripples it to some degree. It came to me on my brother's HDD. Why he didn't install DVDA is beyond me but I don't need it. I'm using a little Corel VS11+ authoring program that defaults to MP2 but can easily make Dolby Digital.

I've also made a blu-ray novelty disc with 20 more productions on it...

[jman98]

Yes...I know all that compatibility crap...which is all it is.

I probably should have asked how much I lose per re/trans-encoding MP2 and AC3 audio using the same bitrate.

You lose 16.87965431869542387926435324328974329434233242343 2% on the official Dumbass Conversion Scale.

I'm done here. You're not serious. That much is clear.

[lordsmurf]

What's with all the old-timers poking each other in the eye?

How much quality will you lose?
If you use math, sirens will sound, the sky is falling, and the end is nigh.
If you use your ears, usually nothing.

Audio "quality" is mostly affected by speakers, DACs and decoder chipsets anyway.
Higher bitrates are insurance against loss.

^ Note that what I'm saying here ONLY applies to this conversation !!!