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Old 14th April 2002, 01:23   #1  |  Link
Deptmaster
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AC3 in MP4!

Does anyone know if MP4 will support AC3 as well as AAC?


edit by bond: As of August 2008 the official ac3 specs now include in annex f the specifications for how to place ac3 and eac3 in mp4:
http://webapp.etsi.org/WorkProgram/R...p?WKI_ID=28541

Last edited by bond; 5th September 2008 at 19:00.
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Old 14th April 2002, 01:34   #2  |  Link
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the mp4 muxer on my site supports mp3, aac and ac3 input.. I cannot guarantee that standalones will eventually support that.. very much is still in the designing phase.. if I remember correctly the specs only contain aac.. but maybe due to the fact that there will be devices also capable of playing AC3 it may be possible to use that audio format. But at this point.. nobody really knows.. and those who are working on creating devices usually cannot share what they know until there's an official press release
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Old 15th April 2002, 00:14   #3  |  Link
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This thread contains useful info about this topic. Basically AC3 can be muxed, but not supported by the ISO spec. Anyways, AAC is far superior to AC3, and at lower bitrates, so there should be no good reason to do that.

http://forum.doom9.org/showthread.php?s=&threadid=19497
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Old 18th April 2002, 07:58   #4  |  Link
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In some cases its not really worth it to me to re-compress the AC3 which is already fairly compressed in some cases (2channel@192kB/s) to save a little space and loose alot of quality. This is usually on the case with anime series and movies i cherish. But i do agree that 5channel AC3 on most filmed movies is necessary to downmix and re-compress so AAC is ideal in those cases.
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Old 18th April 2002, 09:47   #5  |  Link
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For my best knowledge the ISO supported Codecs for MP4 are: AAC LC, AAC Main, AAC LTP, AAC SSR, AAC LD, ER AAC (LD), CELP, TwinVQ and PCM raw.

Nobody knows yet what future hardware players will support. The only leads i found were from Ivan Dimkovic (Psytel):
Quote:
Originally posted by Ivan Dimkovic

Audio object types supported are MPEG-4 audio object types:

AAC (Main, LC, SSR, Error Resilient, Low Delay, Scalable...), TwinVQ (VQF), CELP (Speech Codec), Synthetic Audio (similar to midi/wavetable) and even PCM data - you can put as many audio objet tracks as you want...
Ivan Dimkovic seems to recommend AAC-LC for now:
Quote:
Originally posted by JohnV
Yes, Ivan also said to me that he recommends the use of LC-profile with MP4 streams, because it's the only profile supported by hardware devices (at least at the moment).

Of course multi-channel audio is also possible.
(Quotes from the developer forum on hydrogenaudio.org)
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Old 19th April 2002, 22:23   #6  |  Link
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Thanks guys, very useful information ... reminds me i wnated to invite ivan to come here by time ...
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Old 21st April 2002, 00:24   #7  |  Link
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Quote:
Originally posted by Deptmaster
In some cases its not really worth it to me to re-compress the AC3 which is already fairly compressed in some cases (2channel@192kB/s) to save a little space and loose alot of quality. This is usually on the case with anime series and movies i cherish. But i do agree that 5channel AC3 on most filmed movies is necessary to downmix and re-compress so AAC is ideal in those cases.
I understand that AC3 whether it is 2 channel 5.1 or 7 it a 5:1 compression ratio. MP3 at average bit rates is usually about 10:1. And AAC can beat MP3 at lower bitrates than MP3. So by keeping the AC3 yes you would save time. But AC3 at 5:1 has relatively few errors or loss. And recompressing at a propper bit rate should incur very little loss. So recompressing to somethin like AAC would take a bit more time, but would leave me a ton more room to max out the bitrate on the video(Anime needs all the video bit reate it can get!). That way I could have the best visual quality as well as audio quality for my cherrished anime. A little extra time means nothing to me to get something done right. Did I get anything wrong?
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Old 21st April 2002, 04:23   #8  |  Link
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if you kept the original ac3 along with a video stream like xvid, all you would have to do to get an mpeg-4 compliant file in the future when standalone players are available and such files become needed would simply be to transcode the audio to aac or something and then mux the new audio and old video streams together, right? and then you get to take advantage of the latest in aac encoding technology and whatnot, while not losing any of the original ac3 quality. so from this standpoint, regardless of whether or not mp4 supports ac3, it's the most flexible solution for the future.
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Old 30th September 2006, 06:54   #9  |  Link
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Is there now any official way of muxing AC3 into MP4?

I'm encoding my library with x264 @ Q24, which looks fantastic, but when I encode my 5.1 AC3 with nero cmd encoder at @0.30, which appears to be a good balance between size and quality, I end up with a 5.1 audio file within 100MBs of the AC3, so I may as well keep the origional.

Turns out AC3 seems to use about 64kb/s per channel? Which appears to be reasonably efficient?

TIA
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Old 30th September 2006, 09:51   #10  |  Link
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Quote:
Originally Posted by LiFe View Post
Is there now any official way of muxing AC3 into MP4?

I'm encoding my library with x264 @ Q24, which looks fantastic, but when I encode my 5.1 AC3 with nero cmd encoder at @0.30, which appears to be a good balance between size and quality, I end up with a 5.1 audio file within 100MBs of the AC3, so I may as well keep the origional.

Turns out AC3 seems to use about 64kb/s per channel? Which appears to be reasonably efficient?

TIA
there is no way to mux ac3 in mp4 and thats a good thing

when you want to combine avc with ac3 use mkv (or theoretically mpg would also make sense as hddvd uses it)
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Old 25th January 2007, 08:15   #11  |  Link
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Added a "Coming updates" -section for some hints what can be expected in the near future.
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Old 1st February 2007, 17:45   #12  |  Link
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JohnV...

Anything more you can "share" or hint?
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Old 5th February 2007, 17:44   #13  |  Link
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Quote:
Originally Posted by sjchmura View Post
JohnV...

Anything more you can "share" or hint?
I'll do regular updates to the new section.
One remarkable thing is that Cinema-AVC and HDTV-AVC NeroDigital profiles will be officially supporting multichannel AC3 audio. I think this will be a special interest for many who want to archive HDTV tv-streams, or re-encode (unencrypted) blu-ray/hd-dvd into smaller size stream. Skipping the re-encoding of the audio to AAC will also speed up the overall encoding process.
The AC3 support for NeroDigital MP4 will come before the summer.
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Last edited by JohnV; 5th February 2007 at 17:49.
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Old 5th February 2007, 17:51   #14  |  Link
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Those changes we all forgot about last month...

Version number 2.4.5.0

Release Date: 01-18-2007
Changes/Bugfixes

* Under Windows, the Data Files tab was not correctly drawn in Aero mode


Version number 7.7.5.1

Release Date: 01-18-2007
Changes/Bugfixes

* Under Windows Vista, Windows Movie Maker crashed if Nero was running in a few cases
* Burning a compilation to the image recorder was not possible in some cases
* Improved AC3 encoding
* Preview of AC3 files was not possible in some cases
* Nero Burning ROM could not always read the previous session of a multisession disc
* The size bar was not updated when using "continue multisession disc" feature
* Audio books could not be burned on CDs in some cases
* A misleading error message was displayed when trying to use a folder that did not exist


Is Nero embarrassed about these updates? Why are changes posted 3 weeks later?
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Old 6th February 2007, 00:06   #15  |  Link
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Quote:
Originally Posted by JohnV View Post
Skipping the re-encoding of the audio to AAC will also speed up the overall encoding process.
The AC3 support for NeroDigital MP4 will come before the summer.
yeah, saving 7 minutes is a good thing for skipping interoperability

edit: JohnV, you shouldnt forward every nonsense request you hear on boards to your developers and bosses
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Old 6th February 2007, 09:13   #16  |  Link
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Quote:
Originally Posted by bond View Post
yeah, saving 7 minutes is a good thing for skipping interoperability

edit: JohnV, you shouldnt forward every nonsense request you hear on boards to your developers and bosses
Any speed up is a good thing, especially if you want to include multiple audio streams, though our next AAC encoder version should be 20-25% faster.

Sorry bond but you are wrong, this was not my idea nor my forwarding, but it is a very good idea, since many people want to preserve the original AC3 track of HDTV tv-streams and use AVC (very clear trend out there), don't have to use mkv, and future hardware supporting these specific 2 high profile ND-AVC profiles will play it.. You can always keep interoperability by using AAC if you want, this is just added flexibility and choise for users. And notice that this AC3 option will be available only for the 2 highest Nero Digital AVC-profiles, not for Nero Digital ASP or "lower" AVC-profiles.

Hopefully also Haali, MPC's and VLC's etc. splitters will add support for this new addition when it comes out.
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Last edited by JohnV; 6th February 2007 at 11:04.
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Old 7th February 2007, 02:00   #17  |  Link
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I think the problem is AC3 in mp4 is not part of the spec for mp4. So now special workarounds in every demuxer has to be made.
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Old 7th February 2007, 03:16   #18  |  Link
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specs are nice for the vast majority of hardware producers ... but ahead/ nero build their own units thus are able to play their own content... if the user/ buyer is satisfied with the result - TRUE 5.1 digital sound without analogue loop ways - the user is the last one who cares about specs
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Old 7th February 2007, 03:18   #19  |  Link
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well, i wouldnt call them "workarounds" but support for AC3 private streams.
Private streams are also in the specs, so it's not completely out of specs...
It's just a "private" solution but since there are tons of ac3 decoders it would suffice to implement private streams parsing in the splitter and "connect" the ac3 decoder when necessary.
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Old 7th February 2007, 11:41   #20  |  Link
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Yep... that's right..

Unlike with situation with the .AVI container, it's not like "private streams" in .MP4 are an out-and-out hack

The placing of VOBsubs subtitles within MP4 as a "private stream" has, by all accounts, proved to be a very useful implementation. As it makes use of the original subtitle decoder engine, installed within all MPEG-4/DVD players.

Placing AC3 within MP4 as a private stream and have it use the original AC3 (or even DTS) decoder engine, installed within all MPEG-4/DVD players seems a very logical step forward.... And far more understandable for end-users.
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