Dolby Digital 5.1 and DivX

[brashquido]

Hi There,

These are probably really stupid questions, but I'll ask anyway.

1) Is there any way to store the audio in a DVD > DivX conversion in Dolby Digital 5.1?


2) If the answer to the answer to the first question is yes, what size in MB with the Audio take up approximatley?

Thanks

[jggimi]

1) Is there any way to store the audio in a DVD > DivX conversion in Dolby Digital 5.1?Yes. "ac3" format audio is dolby digital. I don't know what toolset you use for encoding... but if you use dvd2avi, it can demux ac3 streams into individual ac3 files, with the delay or advance in milliseconds as part of the file name. Nandub can then be used to interleave the ac3 into an avi format file. Doom9's guides can show you how.
If the answer to the answer to the first question is yes, what size in MB with the Audio take up approximatley?It depends on the number of tracks and the length of the soundtrack. I also don't have any ac3 files handy at the moment, but I seem to recall 5.1ch taking 448kbps. I haven't seen a poll, but it seems to me that most forum members who use ac3 sound in avi files typically do 2-3 CD sized transcodings.

[brashquido]

Thanks for your reply jggimi. :)

I use FlaskMPEG to do my encoding. I'll check out that guide. Thanks alot. I usually convert my movies to DivX of about 700 MB in size so they fit on a single 80 minute CD. I'm planning to use the 99 minute media for my future conversions and use the extra 200 odd MB to store the audio in dolby digital if possible. Just depends on the size I spose.

[brashquido]

Don't know how I missed that before! Your able to just select direct stream copy in FlaskMpeg to have Dolby Digital in your DivX movie. It's just the size that'll be a stumbling block I'd say. Thanks again jggimi!

[Acaila]

Since AC3 is usually rather big (384 or 448 kbps, which ends up at around 250-350MB) you could transcode the 6 channel AC3 to 6 channel Ogg Vorbis at a lower bitrate. Starting with 192 kbps and probably around 200-250 kbps you'll get a good quality 5.1 channel audio file at a more reasonable filesize.

[brashquido]

Thanks Acaila,

That sound really good! That'd mean I wouldn't have an AC3 file any bigger than about 250MB, leaving atleast 650MB for the video which should be enough for good quality. I was lead to beleive in another thread I posted here (http://forum.doom9.org/showthread.php?s=&threadid=23704) in the Audio forum that Ogg Vorbis files only work with specific hardware. Is this true?

[outlyer]

Originally posted by brashquido
Thanks Acaila,

That sound really good! That'd mean I wouldn't have an AC3 file any bigger than about 250MB, leaving atleast 650MB for the video which should be enough for good quality.

If you want to get some extra bytes you can transcode it to a lower bitrate, as posted in the thread you link you can't decrease the bitrate *a lot*.

I was lead to beleive in another thread I posted here (http://forum.doom9.org/showthread.php?s=&threadid=23704) in the Audio forum that Ogg Vorbis files only work with specific hardware. Is this true?

Well, I don't really know if it only works on analog 5.1 sound cards (anyway I don't have digital speakers so I can't test), all I know is that the channel mapping is fixed (or at least it was some time ago, filters get evolved fast :) ).
Anyway my opinion is that you should try OGG, you get the *lovely* features (instant seek, almost no interleaving overhead, and NOW chapter support... and so on... :D ) and OGG Vorbis (audio) can go lower than MP3 in bitrate with enough quality... SOOOOO do a test, maybe a short clip, enough to 'hear' the difference, and try AC3, transcoded AC3 and OGG Vorbis to see what fits best your need.

Subjective tests are highly recommended here :)

[brashquido]

Thanks outlyer,

Just a few more questions. I have a Yamaha RX-V520 (http://www.yamaha.co.jp/english/product/av/products/ht/rxv520.html) Digital Home Theater Receiver that has 6-Channel External Decoder Input Terminals which I beleive Ogg Vorbis can use. My question is what hardware on the PC side of things do I need to interface via this method seeing as though SPDIF isn't supported.

Last question. If I encode the audio in the vorbis file, will my amp recognise it as a Dolby Digital format?

[Acaila]

Seeing as this is in fact an audio question, it'd be more suitable in the audio section. Hopefully the audio experts can answer you questions.

[MaTTeR]

Originally posted by brashquido

Last question. If I encode the audio in the vorbis file, will my amp recognise it as a Dolby Digital format?

No. Your amp will need to be set to a multi-channel mode. You should have a sound card that has capable 6ch analog outs and then hook them to the respective ports on your amp. Your amp will not recognize this stream as Dolby Digital, only a true AC3 format would accomplish this ATM.

SPDIF can not carry the multi-channel signal to the external amp. Instead, it would only carry over a 2ch PCM stream.

The hope is that someday amp makers such as Denon, HK, etc will implement Vorbis into the hardware. This would allow us to then send the streams over SPDIF:)

I was lead to beleive in another thread I posted here in the Audio forum that Ogg Vorbis files only work with specific hardware. Is this true?
Again, your sound card must have 6ch analog ports and then your amp should also have 6 multi-channel ports usually in the form of RCA type plugs.

In saying all that, I don't see Vorbis as a multi-channel solution right now. Currently, the developers are working on full channel coupling for multi-channels. Until this is implemented, all we have is a 6ch file with all channels at full bitrate, this is obviously not effecient to say the least. In short, you'll find that 6ch Vorbis files will still be much to large in filesize until we have true multi-channel coupling implemented.

[brashquido]

So if I wanted my AMP to recognize the Audio as Dolby Digital 5.1, and to reduce the size of my AC3 file, the only way would be to alter it with something like soft encode? Other than that I might just have to bite the bullet and use 2 CD's for each movie.

[outlyer]

Originally posted by brashquido
So if I wanted my AMP to recognize the Audio as Dolby Digital 5.1, and to reduce the size of my AC3 file, the only way would be to alter it with something like soft encode? Other than that I might just have to bite the bullet and use 2 CD's for each movie.

Right! Your amp will recognize as AC3 only digital signals in AC3 format (dummy anwer :P), so to make it use a non AC3 track it should be translated to AC3 on-the-fly i guess (:confused: ) and that's not an option.

If you want to go "fully digital" (aka go AC3), yes, the only way is use soft encode or any other app capable of the same operations.

Anyway using 99min media is not a bad idea and you'll have enough space for not-too-much-long movies on 1 CD.

[brashquido]

Hmmmmmmmmm....... Thanks outlyer. That leaves me with the problem of where can I buy a copy of Soft Encode, as I beleive it's not made anymore?

[Antimon]

I would not sugest goign lower then 384 kbs for a 5.1 stream, you'll start introducing artifacts and would be better off goign to a 2.0 ac3 solution.

Pro logic is not that far off from ac3, better to have a 192 kb/s 2.0 ac3 with plenty of room then a highly crucned 5.1 at like 224 or so.
at 384 you're only devoting max 64 kb/s a chanal, qhixh i s basically 128 mp3 for stereo, but it sounds much better :-)

[outlyer]

Originally posted by brashquido
Hmmmmmmmmm....... Thanks outlyer. That leaves me with the problem of where can I buy a copy of Soft Encode, as I beleive it's not made anymore?

Well, that's really a problem, maybe you can find it on the net under the "abandonware" sites, although it's not clear that abandonware is legal, so... :confused:

Maybe you should try using the original AC3 track (if, as it seems, it's so important for you to get the 5.1) and see if the resulting video fits your needs.

As pointed by Antimon it's not a bad solution to use pro logic if you can live without 5.1.

[brashquido]

Yeah, it looks like I'll have to use pro logic if I want to get every thing on a single CD. I spose I'll just have to get my computer together and experiment with it.

[MaTTeR]

It worth noting that the ripping scene seems to be adopting 256kbps AC3. I'd be interested in hearing the feedback if anyone has heard these.

@Antimon
How nasty are the artifacts? I'm curious because I've heard other state this before as well. However, if the ripping scene is adopting this method for 1CD rips then you can bet they aren't hearing the artifacts or using some professional application.

[Antimon]

Honestly i have't checked in thsi case i'm going by more of a bit theroy then listioing tests, i'll get back to you on that.

but to be honest unless you can get it down really low, like from 384/448 to 192/224...the decoding/encoding time is enterily counter productive and very hard drive sapce demanding as it has to decode the ac3 into 6 pcm wavs then re encode it, we're talking hours here.
i'll post exact numbers for my now inspired testing

[Antimon]

I'm....I'm Shocked.....

Hell who needs vorbis!

Ok here's the deal, now keep in mind i have a smaller system. The clip was chapter 30 from True Lies. It features multiple explosions, rocket, suround bullet hits, underwater swimign with fireball flying over head, and a gas tanker turned into a flame thower. Audio goes form suroudn sound panning voices, breaking bones, bullit hits on wood and metal from a machine gun, water etc pretty full frequency and dynamic range:

224: Lowest allowed setting for 5.1 audio
I'm surprized as hell but their are no compresion artifacts.....Not in the traditional low bit rate mp3/aac/mp2 sence...

There is a loss of fedelity best i can describe it...it's like converting to 22khz audio *even though it's still at 48*

But there is no noticeable channal bleeding or loss of positional information, and no "i'm compresed" artifacts.

The other characteristic is degraded lfe, esepcialy at low volum levels it seems to be a bit cliped but not that bad. Amazing...

256: Next allowed bitrate

The fidelity shoots way up, and the lfe is much better defined andpresent...so much so that from here+ the quality increase seems almost negligable, and you start getting into diminished returns on file size increase/quality increase.


I also tested 320 and 384 *384 isjust as common as 448 for pro dvd 5.1 bit rates*

I can;t make any clar cut comentable distictions between them and the 448 sorce.

Now th ebad news. The clip was 5:58

Besweet transcoded it in 48 seconds into 6 waves which i HIGHLY recomend because soft encode took 1:20 just to demux the wavs then more time *negligable on such a short clip* to render teh audio peaks, whcih it has to do anyway whether it's openign it's temp wavs from the ac3 or the waves created by besweet's 6 wave option. Also besweet gives you greater flexability with where they go, and can be stoped.

the temp wavs took 198 meg , for a 6 minute clip.....33 meg a peice

the re-encoding process varried which surprized me...

224 - 3:20
256 - 4:06
320 - 4:05
384 - 4:29 and as a compatablity check
448 - 5:32
*it should be noted they wer eencoded in that order without reboots inbetween

file size:
Wavs - 198 meg *ac3 rocks*
448 sorce: 19.1 meg
448 re -enc: 19.1 meg
384 - 16.4
320 - 13.6
256 - 10.9
224 - 9.6

[canadian_fbi]

wow, so you went from 384 to 256 with basically no noticeable loss in quality? and i have the true lies dvd, and that scene must be a huge test for the encoder. that's pretty impressive. unfortunately i won't have my dolby digital system near my computer for another couple months till i get a new place or i'd test it out. i don't want to go taking the hours and gigabytes to transcode ac3 files unless i can hear for myself that there's practically no difference, but 128 kbps saved is nothing to scoff at. :)

[brashquido]

That's great news! I was a bit worried the fact that a 5.1 encoding at 224 only has about 9kHz of bandwidth to play with would mean that the high and low frequency's would suffer a fair bit. Sounds like 256 might be the sweet spot though.

[Antimon]

the sourse was actually 448 for this particualr dvd :-)

i didn';t have the voluem very high eithe rmidn you but just the fact that it's seemingly compresion artifact free is a big plus thats worse then missing frequencies for sure.

listinign in pro logic mode in headphones also backs up the missing frequencies at 224 and virtually non noticable differnce between 256--448 Lets put ti this way i'd pick a 5.1 at 256 over a say 192 mp3. thats only 48 kb/s over stanmdard 224 mp2 audio, and it adds 3.1 chanals, impressive.

One thing i wanted to ention though in powerdvd the time stamps are messed up...the lwoer the bitrate...the shorter the file's length is reported..but it plays normally and it counts corectly but you get like playing 3:40 out of 2L45....it's weird
hopefully it wont be affected by muxing.

Does anyone know where ac3 fits in? Is it more simerly related to mpeg audio? or closer to like oog...while we're at ti, whats oog like? hehe

just curiose, i dont expect anyone to know and be ablle tp explain it simply :-)

[MaTTeR]

:D Nice work and very nice feedback Antimon.

I'm off to work now but will reply later.