AC3 vs. PCM on DVD-R...

[rlhartman]

I've RTFM'd as much as possible and found a LOT of useful info on this site (a big Thank You to everyone who contributes here). However, there are a few areas relating to audio on DVD video discs on which I've found little, or conflicting, information.

My setup: Sony TRV38, P4 2.4GHz / 1.5GB with dedicated video hard drives, XP SP1, Premiere 6.5 for editing, Premiere's MainConcept MPEG encoder, Ulead MovieFactory2 for menus and directory structure, Nero for burning, Pioneer DVR-A06. I don't lose frames during capture and can burn discs with no problems. My questions relate to content preparation (really, data manipulation), not the mechanics of input and output.

1) It's clear that DVD's require a 48KHz sampling rate. But at what bit depth? Can you use 12 bits instead of 16 to save 25% space right off the top, if dynamic range isn't important?

2) PCM audio consumes a lot of space. AC3 seems to be the preferred solution to that, since it's officially supported by the DVD spec. How to get from PCM (or .wav) files to AC3? The main tool I've seen for this is BeSweet, but there's a comment on this site which specifically says its output has compatibility problems with some players. The whole reason for going to AC3 is to avoid compatibility problems... otherwise I'd use MPEG. I notice that TMPGEnc has an optional AC3 encoder, but does it make sense to use that solely for audio work? Does it, too, suffer from compatibility problems? Should I even bother with AC3, or just stick with PCM?

3) I only work with mono or (at most) stereo audio - my camcorder doesn't capture 5.1 [grin]. I've read comments which say going to AC3 for mere stereo doesn't make sense. Why not? If AC3 delivers good quality and compression, why can't that work for just two channels? What am I missing here?

4) Can you switch audio encoding schemes in mid-track? Say I've got a track that has some audio which can be low quality, and other sections which need to be higher quality. Video can change its effective bit rate when the encoder detects more motion - can audio do the same? Can the author exercise any control over this, since a human can make conscious choices about what audio needs to be favored?

Thanks in advance for comments and advice.

[wulf109]

PCM is part of the DVD spec. and all DVD players support PCM in addition to ac3. PCM is commonly found on concert DVD's. PCM is uncompressed and ac3 is compressed. For music PCM is noticeably better then ac3. When I encounter a concert DVD that has only ac3,I convert it to PCM.
I've tried Besweet and ffmpeggui and both do a poor job converting to ac3. MPEG audio is a better option and althought it is not part of the NTSC spec for DVD the vast majority of DVD players support it.

[Soapm]

I think it all depends on what you are doing. In your case, moveis from a camcorder then PCM is not a problem. If you were encoding a war movie and wanted the battle to come from all parts of the room then 5.1 is the best choice. If you have a long movie, over two hours then AC3 will let you use more bitrate for the video.

I make 2.0 AC3 all the time. One reason is I like compression and to normalize the dialog. This allows me to watch my action movies at night without waking up the whole house or constantly turning the volume up and down. Another reason I use AC3 is because it lets me use a higher bitrate for the video.

I use Sonic Encode to turn wav into AC3. However, it is processor intensive and slow.

[turk690]

to rlhartman,
1) DVD audio spec is 16bit. That's fixed so you can't use 12bit or other.
2) You should stick with AC3 for the best compatibility and efficient use (longer playing time) of your DVD-R space. It's true that BeSweet does produce AC3 audio streams some older players balk at. The TMPGEnc DVD-Author AC3 plug-in, IMHO, is priced just right to produce full-fledged, official, right-to-spec 2-ch AC3 streams even older players should be happy with. Compare this with some other AC3 plug-ins (for, say, Premiere, that cost $hundreds). Maybe you should consider Adobe Encore which has a legal 2-ch AC3 encoder built-in (bundled with ADSTech Pyro Pro FireWire card, Audition, Premiere Pro for the cheapest way of getting it). Lastly, if your program is less than 90mins you can even get away with PCM.
3) Dolby Digital/AC3 has been designed to use bits ACROSS channels where they are deemed more in demand. It's possible to have a full-bore 5.1-ch DD AC3 stream, as well as 4-ch, 2-ch, 3-ch, and even 1-ch. It's silly saying stereo (2-ch) DD streams don't make sense. If it works for 5.1 surely it will for 2. You scarcely missed anything.
4) As far as Dolby Digital is concerned, audio encoding DOES and CAN changed midtrack. For example, a 5.1ch DD stream is 448kb/s. This is an overall constant bitrate. Inside the stream, however, DD algorithms constantly determine which of the channels at the moment requires more bits and accordingly allocate these to that/those channel/s. In completely professional DD encoding setups a bitrate meter shows how much bitrate a channel is gobbling up. In most movies, so I've read this is the center ch. Which of the channels are active and for how long will determine for one what overall bitrate the DVD-author will use. That's why some 5.1-ch movies require 448kb/s, while others only 348kb/s. For 2-ch you might encounter 192kb/s, 224kb/s, and 256kb/s.

[rlhartman]

Excellent feedback - thanks everyone!

I've now tried to use AC3 audio, and while the resulting audio files are substantially smaller the finished image size (as reported by Ulead MovieFactory 2SE) doesn't change a bit.

I tell MF2SE to bring in the video file, then I explicitly tell it to "replace the audio" on that file with the associated AC3 file. There is zero change in the projected image size on the disc... which is thus too large to fit on a single DVD-5. If I could get MF2SE to respect the smaller audio files, it would all fit without me having to reduce the video bitrate below 6Mbps.

Let me say that a different way: When I "replace" the audio, the projected disc size neither shrinks (as it should if the M2V file contained PCM audio) or grows (as it should if the M2V file contains no audio at all).

I'm stumped. MF2SE sure looks like it supports bringing in M2V files and then associating my choice of audio with them, but in practice I don't seem to be getting that result.

How do I get MF2SE to take advantage of the dramatic size reduction going from .wav to .ac3 files?

Thanks!

[rlhartman]

I'm wondering if Ulead MovieFactory 2SE transcodes all audio to PCM. MyDVD expressly says it does this, and while I can't find anything in MF2SE's docs which say so it's the only explanation I can fathom.

Here's what's happening. I go into MF2SE and bring in the three M2V files. Their total size is just over 3GB. If I don't "replace" the (nonexistent) audio, the projected disc size stays right at 3GB.

If I then go back and "replace" the audio, and bring in the associated AC3 files, the projected size balloons to somewhere between 5GB and 7GB (it varies depending on the order that I do things in MF2SE). The hard drive size of all three audio files is 171MB, so (3GB + 0.171G) should be well within a DVD-5's capacity. Yet MF2SE blows it all the way to 5-7GB.

The only explanation I can come up with for this bizarre behavior is that MF2SE is transcoding the AC3 to PCM. Why?!? By definition they can read AC3 if they can transcode it - why not just use it as-is?!?

Arrrrggghhh!

More importantly - what tool supports this type of work? I need to create chapter points within imported M2V files (which is why I went from MyDVD to MF2SE in the first place), and keep the price low.

Thanks!

[freestyler]

When I encounter a concert DVD that has only ac3,I convert it to PCM

Why would you do such a thing? All you get is a bloated uncompressed stream of a compressed source

[bugster]

I'm wondering if Ulead MovieFactory 2SE transcodes all audio to PCM. MyDVD expressly says it does this, and while I can't find anything in MF2SE's docs which say so it's the only explanation I can fathom.


Thanks!

I dont use MF2 but have read posts on these forums that suggest you are partly correct in your assumption. MF2 will support Mp2 audio or LPCM but does not accept Ac3. Though I believe there may be a registry Hack that will allow it to do so. Search the forum for it, I am sure I saw it somewhere.

[turk690]

If MF2 does indeed change AC3 streams to PCM then it has means of detecting them, reading and decoding them then encoding them to PCM; how kvetchy and wily of Ulead to do so and surely they just want u to buy their AC3 plug-in, among other things (when it already has means of manipulating AC3 streams within). Not bad, but they should be more upfront. MyDVD outright deals only with PCM and MP2 and doesn't accept AC3, period; Sonic is clear about this and says if u want AC3 then get DVDit! PE. You try Adobe Encore (VERY steep learning curve, not unlike hiking a 60deg cliff face, but very well worth it), or TMPGEnc DVD-Author with its much better value (and legal-stream producing) AC-3 plug-in.

[FOO]

I think its possible to get MF2 to accept AC3 if you mux your audio and
video into a System stream first.

[rlhartman]

Two questions:

1) Does TMPEGEnc's menu creation abilities match or exceed those of MF2SE? That's why I went to MF2SE in the first place: It permits you to create chapter points within imported titles. I must be able to do that.

2) How would I mux an M2V and AC3 file together so that MF2SE might use them together?

Thanks!

[FOO]

TDA and MF2 have similar fixed (bad) menus.
You can put chapters anywhere with either of them
TMPGenc will mux elementary streams

[hech54]

Here are your answers about Ulead MF2(I think):

http://www.dvdplusrw.org/cgi/forum/ikonboard.cgi?s=964ec247fcd41a50e26d460ff2b785a9;ac...=ST;f=7;t=9854

http://www.dvdplusrw.org/cgi/forum/ikonboard.cgi?s=964ec247fcd41a50e26d460ff2b785a9;ac...=ST;f=7;t=9192

http://www.dvdguideuk.dsl.pipex.com/

I only use MF2's "Edit Disc" function...so my AC3 sound arrives on my finished product intact.

[MOVIEGEEK]

Sonic MyDVD 5 Deluxe will encode to 2ch AC3,there is also a AC3 plugin for TMPGEnc DVD Author.

[rlhartman]

My version of MovieFactory is "2.10.2153.1160 SE" (from its About page). One of the references mentioned above implies that some versions of V2.x will pass AC3 audio through, but later versions (and those patched with something available from Ulead's FTP site) "correct" that.

Here's the quote:

"Note: Do NOT install the update patch found here [URL]. This patch closes a loophole in the original version which allows AC3 sound to pass through without re-encoding the audio, resulting in losing the sound. The full version 2.1 product does support the pass-through of AC3 sound, so you should be ok."

I have not been able to find anything on a registry hack which will permit AC3 to pass through. Anyone have anything more on that?

I'm now on the hunt for a tool which will mux V+A together. According to one response above, TMPGEnc will do it, and I'm hoping to find others too.

[rlhartman]

Apparently I installed (and then removed) TMPGEnc's DVD Author program a while back, when I was just starting with DVD stuff. Their timestamp is still on my machine somewhere and it believes "my trial period has expired". Thus, even with a fresh download and install, I can't test it to see if it will permit me to use existing MV2 + AC3 files. [sigh]

I checked the trial version of the latest MovieFactory (V3), and guess what - its main restriction is no support for AC3 files. I don't know if that means it won't **generate** AC3, or if it also won't **accept** incoming AC3 files... but it sucks that the ONE feature I'm seeking is disabled. [growl]

Everyone and everything is conspiring against me, it seems. Yikes!

Any OTHER tools I can try?

[FOO]

Ifoedit can make DVDs with no menu . it's free

[rlhartman]

Thanks, but I need to create menus with chapter points.

Anything else to recommend?

[rlhartman]

OK, here's the latest.

I created the elemental video and (PCM) audio using the MainConcepts MPEG encoder. I then transcoded the PCM audio file to AC3 using ffMPEG. Next, I muxed the M2V and AC3 files using bbMPEG, resulting in an MPG file whose size seems appropriate.

Viewing that MPG file using Windows Media Player, the audio is very choppy... it cuts out quite frequently for a fraction of a second. It's hard to tell, but it seems like it's when there is a large *relative* change in audio amplitude.

Nevertheless, I then used MovieFactory 2 to create the VIDEO_TS directory structure. It warned me about the audio associated with the MPG file, but carried on nonetheless and generated the VIDEO_TS structure without mentioning any errors.

Viewing the VIDEO_TS structure with a software DVD player, it still has the audio cutout problems. The audio is properly sync'd... it just has "dropouts" all the time.

I'm burning it to DVD-R as I type this, and I'll try it on my standalone DVD player. Having failed two out of two tests, though, I don't expect it to be any better.

All of the above tools are highly recommended on this site. What could be causing the audio dropouts? The original PCM audio file is flawless.

[rlhartman]

Interesting... I burned the VIDEO_TS structure to DVD-R and it worked fine in my standalone player. The audio had no dropouts.

On my primary workstation (2.4GHz), playing it back consumed only ~25% of the CPU but it had dropouts. On my laptop (1GHz), it consumed ~50% of the CPU and also had dropouts. In other words, neither machine was anywhere near maxed out (and they both play other DVD's, commercial w/ AC3 and homemade w/ PCM audio, just fine). The disk subsystem wasn't maxed out, either. I don't think it was a data bottleneck problem.

Any ideas why it would have dropouts when played back on PC's, but not on a standalone DVD player? I'm using Ulead's DVD player, but if it had a problem decoding AC3's it would have it with commercial ones too. Unless ffMPEG's AC3 output is troublesome on other platforms, too, and not just Pioneer drives...?

[rlhartman]

I should have also mentioned that Ulead's DVD player app properly plays DVD's which have been copied to the hard drive of both machines. Since those commercial DVD's are almost certainly using AC3, that exonerates Ulead's player and the disk subsystems on both boxes. I suspect it's a data encoding error, probably within bbMPEG when it converts the PCM to AC3. My question is, why does it show up only on PC's but not on standalone players?

[lacywest]

Intervideo WinDVD Creator 2 ... does a nice job convert videos with AC-3 audio

https://www.videohelp.com/forum/viewtopic.php?p=789502#789502

[MavDVDR]

Apparently I installed (and then removed) TMPGEnc's DVD Author program a while back ... thus, even with a fresh download and install, I can't test it to see if it will permit me to use existing MV2 + AC3 files.

it will take m2v & ac3.

I need to create menus with chapter points.

it will do that as well. The templates provided are fairly basic but once you add in a background mpg (video + audio) and use their Motion Menu setup for the Chapters, the end result looks pretty professional.

PS. Vegas Video ($) does a good job of converting wave to fully compliant ac3. Besweet (free) can also do this but you wont hear sound if playing the resultant DVD with Win DVD, Power DVD or some standalone players.

But since your original audio is mostly mono (and the smaller file size is your predominant reason for wanting ac3), have you considered mp2?

[rlhartman]

Yes, I've considered MP2 audio but I'm concerned about the compatibility problems. It's not part of the official DVD spec, so while it *should* work most of the time, AC3 is certain to work.

[racer-x]

Why don't you use DVD-Lab? It will easily take your m2v and ac3 and will let you create vitually any menu you can think of. It also has a 30 day trail version you can download.

[MavDVDR]

Yes, I've considered MP2 audio but I'm concerned about the compatibility problems. It's not part of the official DVD spec, so while it *should* work most of the time, AC3 is certain to work.

Of course ac3 is better but it's main advantages are:

1) small file size;
2) multi channel dolby digital; the real sound advantage kicks in with 5 channels.

The disadvantage is that any program that creates fully compliant ac3 is usually expensive (licensing fees). The ac3 plugin for TMPGEnc DVD Author is probably the cheapest option but I don't think it goes above 2 channels. Video Vegas is very good (as are some of the formerly Sonic Foundry range) but the program and ac3 plugin are very pricey.

Ac3's made with Besweet have the same "compatability" issues u think u might have with mp2. See this Thread.
https://www.videohelp.com/forum/viewtopic.php?p=754657

I completely recommend ac3 for DVD authoring ... but u need the right program if you're interested in broad compatibility. Having said that, if your source sound is only mono, I don't think you'll have any problems with mp2.

[rlhartman]

I only ever work with two channels anyway, so that's not a limitation for me.

I'm strongly considering TMPGEnc's Author program and its AC3 option as a compatibility improvement over ffMPEG. Any experience with that? Do you (or anyone) know about compatibility issues and TMPGEnc's AC3? Is it better than ffMPEG?

[Nolonemo]

Ulead DVD Workshop 1.x (without the ac3 plugin) accepts pre-muxed m2v and ac3 streams. I've done lots of stuff no problem, used TMPGENC to do the muxing.

[rlhartman]

Thanks for the tip. My current experiments show that Ulead's VideoFactory 2SE will also accept pre-mux'd M2V+AC3 files, though it complains about them a bit. (Thanks for those on this site who suggested I try such approaches.)

What's interesting is that it DOESN'T like pre-mux'd MV2+PCM. My current project has a slideshow with an audio track, and it's short enough that I'm just leaving it in PCM. Since I was muxing the much longer M2V+AC3 titles anyway, I figured I'd go ahead and pre-mux the M2V+PCM as well.

Bad idea. MF2SE choked big time on it. Every click of the mouse drove the CPU to 100% for minutes at a time, no matter what I was doing. Even if the current action didn't directly involve the PCM-based clip at all.

Duplicating the project, with the sole exception of separately importing the M2V file and then "replacing" its audio with the PCM, fixed this behavior. MF2SE no longer went to 100% CPU all the time and I was actually able to get things done. So now I'm pre-muxing titles which use AC3, not pre-muxing titles which use PCM, and all seems well.

Interesting behavior, eh?

[MavDVDR]

I only ever work with two channels anyway, so that's not a limitation for me.
I'm strongly considering TMPGEnc's Author program and its AC3 option as a compatibility improvement over ffMPEG. Any experience with that? Do you (or anyone) know about compatibility issues and TMPGEnc's AC3? Is it better than ffMPEG?

On the pegasys-inc site it says:
http://www.pegasys-inc.com/en/product/tsp_ac3.html

-To specify AC-3 sound for the output:
-In [Environmental settings]: Set "re-encode MP2 audio files to Dolby Digital (AC-3) audio" as default, so you can make AC-3 sound DVD-video.

*But AC-3 with 5.1 channels or other multi-channels source cannot be re-encoded.

ie. they only mention the re-encoding of MP2 files to ac3. So I don't even know whether their plugin can convert PCM to ac3. Has anyone tried?

Incidentally, DVDit can convert PCM to ac3 during the vob creation process, but DVD Author's interface is simpler.

In relation to premuxing before authoring, it's just an uneccesary step forced upon you because of the limitations of the programs you are currently using - and not desirable if audio is important. Refer to the Main Window section of this very useful Guide:
http://dvd-hq.info/Compression.html#Main

... but since your source is mono anyway, it won't make any difference for your current purposes.