Need some education on Audio formats used in DVD's (standard and Bluray)

[nzdreamer55]

Hello everyone,

Well I am posting here because after reading the FAQ, and searching the forums I need a little guidance about audio formats that are on DVD's.

I had a lot of DVD TV shows and movies that I have converted to .mkv files using MakeMkv (thank you who ever made this program it rocks). I did this to store on my HTPC so we could watch things without going to find the disk. So far all the conversions have been with regular DVD's, not bluerays. From my reading MakeMkv will take the MPEG-2 stream and just repackage it in a .mkv container. Some of my movies have had 2.0 or 3.1/2 audio. I really don't know how the audio is present on the DVD and thus I'm not sure how MakeMkv handles this.

My goal is to run these mkv files through handbrake to make them smaller, but I just don't quite get how the audio works in all of this so I am unsure what settings I should be using. I really want more understanding of the audio aspect so if you tell me what settings to use I will be thankful, but still dumb.

One file handbrake tells me that the input is AC3 (2.0 channel). So does this mean that the sudio is compressed with the dolby digital technologies and that it is stereo? Is AC3 a format or a container (I think it is a container and the format is something else)? What about othere types of dolby (surround, prologic, etc.)

I think that I want to use ACC (faac codec) as this seems like it is the most advanced codec format?

So as you can see I am really looking to get a better handle on understanding this audio issue so if someone can point me to a simple explination (I realize this is a tough subject) that would be great. Kind of like a class I heard about in collage called physics for poets. Detailed enough, but from a simplistic view to get the initial points.

Thanks
Steve

[redwudz]

Most common is AC3 (Dolby Digital) for DVDs, can be stereo or up to 8 channels. Blu-rays use several formats, the most common probably DTS, usually 5.1 or better for surround sound. For other formats, look to 'WHAT IS' DVD and 'WHAT IS' Blu-ray to the upper left on this page. Make sure your devices can play back AAC before committing to that.

I convert the Blu-ray DTS audio to AC3 5.1 @ 640Kbps for my BD>MKV H.264 conversions. The AC3 is compatible with most all players. For DVD>MKV, I use AC3, usually 192 Kbps up to 448Kbps for 5.1. I usually just copy the existing AC3 audio to the MKV.

[yoda313]

Most common is AC3 (Dolby Digital) for DVDs, can be stereo or up to 8 channels

I don't mean to nitpick too much but I though 6.1 was the max for dvds (7 channels)?

Is 7.1 a theoretical maximum for dvds?

edit - were you browsing the what is dvd section maybe? I did look up and it said up to 8 audio tracks. Is that what you meant?

I would be interested interested to know if 7.1 is feasible on dvd. But I don't know if it is.

[nzdreamer55]

Thanks so much redwudz. So I took a look at the What is DVD and got the following:

Audio
48000 Hz
32 - 1536 kbps
Up to 8 audio tracks containing Dolby Digital, DTS, PCM(uncompressed audio), MPEG-1 Layer2. One audio track must have MPEG-1, DD or PCM Audio.

So I kind of get this. With the Dolby Digital is AC3 a container that holds the number of tracks 2-8? Handbrake make it seem like the encoder is ffmpeg that is used to put the audio into the AC3 container. Maybe this is usefull if it originally starts as PCM, DTS, or MPEG-1 layer 2? It also allows for pass through of the AC3 which kind of makes it seem like a container.

Is ACC a new or old format/container? You said that I need to make sure that my device can play it back so I guess it isn't very widely used?

My HTPC will be sending the audio via HDMI cable to my TV and from there to a sound bar (so the TV kind of acts like a receiver) via a Toshlink optical cable. Right now the AC3 (2 channel) works fine so I think that the TV might decode it and pass it to the speakers ina PCM format? Here are the web site info.

I did read that the device that is sending the audio signal to the sound bar should be either set to AC3 or PCM so I'm not sure what format my TV is putting to the sound bar. It might be just passing the AC3 to the sound bar via the Toshlink or it might be changing the AC3 to PCM and then passing it to the sound bar.

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Steve

[Cornucopia]

To clarify:

Audio on DVDs are ALWAYS muxed into the VOB container.

Think of the VOB container as a special-case Super-MPEG2 Program Stream. (Pgm streams normally can't hold PCM but VOBs can).

You have a choice of 1-8 STREAMS of audio total (per VOB). What format these streams are is left up to the producer, but at least one of them has to be AC3 to be "legal" (Mpeg Layer2 is no longer officially legal).

Formats available are: PCM, AC3 (aka Dolby Digital), MPG Layer2, or DTS (others were offered but never implemnted).

Within each stream, you have a choice of how many channels of audio, which is partly determined by the producer, but each format has a max # of channels - for PCM the theoretical max is 8ch but 2ch is really the normal max, for AC3 it's 5.1, for Mp2 it's 5.1 or rarely 7.1, for DTS it's 5.1 or rarely 6.1.

There are some bitrate constraints that may make you lessen the # of channels.

If you demux audio from its VOB container, you'll usually end up with RAW (containerless) audio streams, although it's pretty simple to wrap the PCM as a standard WAV.
So if you see a file like *.ac3 or *.dts, these are raw streams.

If you see an AC3 or DTS that is 2.0ch, all you know is that it uses 2 channels. It could incorporate:

A. Stereo
B. Dual Mono (both tracks identical to each other)
C. Unrelated Dual Channel (like Separate Voice+Music/FX, or like Bi-lingual, although this is not the standard or recommended way to do this)
D. Dolby Surround/ProLogic/PLII, which a multi-channel stream that has been matrixed down into a stereo-like format

AAC is another Mpeg audio format that was still being developed when they first decided on the DVD spec, so it wasn't ready in time to be included.
It's more complex and more efficient than Mp2 or AC3 (for the same quality), was later improved on and included in the MPEG4 spec.
It's not supported by plain DVD players, so WON'T appear on a regular DVD, though newer model players w/ good chipsets may be able to handle them as standalone files (not related to the DVD portion).
It's usually raw/containerless as well, but can also be used when muxed into an MP4 container (either along with video, or if alone, the container name is changed to M4a or M4b).

If you "set" your player to AC3/passthrough, you can give it a 5.1 channel AC3 stream and it'll pass it along undecoded until it gets decoded by the reciever/soundbar. That way you should be able to hear the FULL 5.1 signal without any loss.
If you "set" your player to PCM, you give it a 5.1 channel AC3 stream and it'll decode and downmix it to 2.0 PCM before sending it down the pipe.
If you're using 2.0 PCM, it doesn't matter what you set it to.

HTH,
Scott

[redwudz]

I don't mean to nitpick too much but I though 6.1 was the max for dvds (7 channels)?

edit - were you browsing the what is dvd section maybe? I did look up and it said up to 8 audio tracks. Is that what you meant?

Yes, should have been audio tracks, not audio channels.

[yoda313]

I don't mean to nitpick too much but I though 6.1 was the max for dvds (7 channels)?

edit - were you browsing the what is dvd section maybe? I did look up and it said up to 8 audio tracks. Is that what you meant?

Yes, should have been audio tracks, not audio channels.

Well actually cornucopia is saying pcm has a 8ch maximum even on dvd.

Can we get verification on that? Would any pre-hdmi amplifier with dd/dts be able to support that?

[Case]

Well actually cornucopia is saying pcm has a 8ch maximum even on dvd.
Can we get verification on that? Would any pre-hdmi amplifier with dd/dts be able to support that?

The DVD FAQ from DVD Demystified agrees with the 8 ch LPCM option. The DD/DTS decoder in amplifiers won't help for PCM audio, as the audio is not DD or DTS encoded. I don't think multichannel PCM will go through the coax or optical cable. That would mean you'll need a different setup to get more than 2.0 from PCM; either HDMI or analog. Analog would require multiple outputs (one for each channel) on the player and multiple inputs on the amp. Not common, but they exist.

[yoda313]

Well actually cornucopia is saying pcm has a 8ch maximum even on dvd.
Can we get verification on that? Would any pre-hdmi amplifier with dd/dts be able to support that?

The DVD FAQ from DVD Demystified agrees with the 8 ch LPCM option. The DD/DTS decoder in amplifiers won't help for PCM audio, as the audio is not DD or DTS encoded. I don't think multichannel PCM will go through the coax or optical cable. That would mean you'll need a different setup to get more than 2.0 from PCM; either HDMI or analog. Analog would require multiple outputs (one for each channel) on the player and multiple inputs on the amp. Not common, but they exist.

Thanks.

So I suppose in theory there could have been a amp with 8 analog rca inputs. Than you could have 7.1 with pcm without needing fiber optic or coaxial for the connection. But I don't know if there were ever any regular dvd players with 7.1 output via rca.

Edit - i know my sony 5.1 amp from several years ago has 5.1 rca input.

[Cornucopia]

Yeah, I can probably count the number of DVD-Video titles with >2ch PCM on one hand. And you'd need an expensive Denon or Marantz, etc DVD player that had ~6ch RCA analog outs (and your reciever had the same RCA ins - mine does).

Not worth the trouble for PCM. You want to work with Multi-channel, use AC3 or DTS. They're well supported (by both players+receivers) and common.

Scott

[El Heggunte]

FWIW, I have an old DVD player which does have 6 analog audio outputs, BUT these work well only for AC-3 Stereo LPCM is OK, but multichannel LPCM goes b0rked, depending on the day of the week , some channels either will be muted or will be swapped.

As for the mentioned "DVD FAQ" --- parts of it have never been duly updated after all these years so it should be always read with some truckloads of salt