View Full Version : basic AAC questions:

14th October 2002, 16:55
...probably belong to the noob forum!!

would probably be good to answer at least some of them in the ac3 -> aac guide since they all came up after i read it!

1) what exactly is AAC? a new codec or some changed form based on the mp3 codec?

2)do i need a seperate codec installed to play aac?

3) can i merge aac sound with an avi with the old nandub method?

4) can i play aac sound files on a mp3 compatible standalone? (probably not i guess :-P)

and just out of curioity:
5) why does aacmachine 'split' the ac3 files in small chunks? any reason for this?

ok that would be it...


PS: as i said total audio noob!! :rolleyes:

14th October 2002, 17:37
1) Yes, I guess you could say AAC is "new", although it has been in development for several years. The reason you probably haven't heard too much about it is because free encoders for end-users are hard to come by due to Dolby's licensing restrictions. AAC is an official audio codec of the MPEG-4 standard. AAC is much better than mp3. You can find out more about AAC at http://www.aac-audio.com

2) Yes. There are Winamp plug-ins for both raw .aac files and true .mp4 files (that can contain AAC) at http://www.inf.ufpr.br/~rja00/ This website also has some AAC encoders and mp4 muxing tools. Quicktime 6 and the Envivio plug-in also play back mp4 files with AAC audio. Get the Envivio plug-in for WMP/Real at http://www.envivio.com

3) No, although Nic tried his best a while back, AAC audio cannot be muxed into an .avi with good results.

4) Don't be so sure! Check out Philips' "Expanium" line of mp3 portables, many of them can play back AAC, although Philips is not hyping this feature.

5) AACMachine is designed to use the Psytel AAC encoder, which has problems encoding very long tracks (like from a movie), so it gets around the bug by breaking up the job into smaller chunks. My experience has been that AACMachine is just as likely to crash, though, as using PsytelDrop to do the whole thing at once. I expect this situation to improve at some point. You can also try using the FAAC encoder, if you can find it, although the consensus is that Psytel produces higher quality.

You can find out a lot more about AAC at http://www.audiocoding.com which has a very nice forum.

14th October 2002, 18:06
first thanks for your help (:
very much appreciated!
i've succesfully installed a winamp plugin and encoded a madonna ac3 sound from a DVD (drowned world tour DVD) into aac just to copare with mp3 quality... is quite amazing!

but still my primary goal is 5.1 sound in avis!
is there any other way to mux an avi with aac?

and: in the decoder folder was an .exe file simply called aacdec.exe in the subfolder ISO. does anybody know what it is for?

thanks for your time!


14th October 2002, 19:12
If your primary goal is 5.1 audio in an avi then why don't you just mux the original ac3 :sly:

15th October 2002, 18:03
good point radicaled!
BUT i just think a little more compression wouldn't be too bad!

but i guess i'll have to stay with that!


4th March 2003, 16:43
There is a way to mux AAC sound into an AVI file. You have to convert .AAC file into a WAV file. Take Nic's AAC DSF from HERE (http://www.inf.ufpr.br/~rja00). It contains an executable that allows to convert .AAC to .WAV (It just changes headders), and also a Directshow filter, so you will be able to mux AAC into an avi file.

I haven't tried it with 5.1 audio, only with stereo, and it worked well.

4th March 2003, 19:33
thanks for the tip
i'm going to see into it as soon as i've got some more time...


4th March 2003, 22:52
My DShow definitely won't work lol :) Back in those days the problems with VBR Audio in AVI wasn't really that well understood (well I definitely didn't understand its weird quirks)

The best AAC DShow filters are probably from 3ivx or borgsoftware, but I havent tried either myself. Im actually quite behind on the audio side of things.

Do people use the 3ivx MP4 filters to play MP4s with XviD & AAC already?


4th March 2003, 23:31
@ Nic, I have tried the borg technology filter and I could not get it to work. Others had similar experience at HA. I use 3ivx direct show filters for playing back xvid and aac. Although, at times it seems to have problems with some of the new developer builds of xvid but it will play it. I think though the general consensus is that 3ivx's filters are the best for this kind of thing. They can't decode 5.1 audio though, just 2 ch.
@ killingspree, you must mux the aac and video into a mp4 container. I suppose it is possible to mux into avi but it is a really bad idea. Take a look at the mpegip project, you can find the utilities to mux it into a mp4 container in the software section. I am not really interested in transcoding ac3 into aac, IMO the loss in quality is quite a bit since the source isn't that great to begin with. In order for it to be worth it you need to reduce the bitrate by quite a bit. I have found that reducing a 448kbps 5.1 ac3 to 256kbps 5.1 aac doesn't sound too bad but I think for it to be useful we need to either transcode from a higher quality source, ie DTS or wait for a SBR implementation of aac which we may be able to reduce the bitrate down to about 192kbps without too much preceivable loss in quality.

5th March 2003, 09:18

There we are again: AVI has its problems with VBR audio. Well, that's a known fact. But there is OGM and also Matroska is now at the door. Do you think - by any chance - that you find the time to change your DirectShow filter to play AAC from OGM's (or Matroska files)? Until now I wasn't able to mux an AAC into an Ogg container, but I also didn't try to hard.



5th March 2003, 10:11
Hmmm, Well the borgsoftware one's opensource (& uses faad which was what mine was based on). Hmmm, do you know Ive never really used OGM...only used for testing.

Ill give it a go,


5th March 2003, 10:52
Well ive got AAC playing from an OGM. Just using the available filters, but I think ill write something to make it a bit easier. Im sure people must have done this before, im off to search the forum.


5th March 2003, 10:58
Didn't the borg thingie use faad 1? Well, I don't know. I don't use OGM for testing, but for backup, Right now if I want 5.1 I keep the AC3, if I want stereo I can use Ogg, so nothing is lost. On the other hand at high bitrates (> 160 kBit) AAC sounds definitely better than Vorbis (to me of course). AAC multiplexing is an option in OggMux by Koepi, but I think it is just there as a future option, so maybe now it depends on you...

[If I just would understand more of that DShow and Windows stuff :mad:]

Hopefully, I don't fall on your nerves with that, Nic. I know you don't have much time (as all of us).


Oops, you've been quite fast with answering your own mail. So I was too slow, anyhow very good news. I don't know if other people tried before, but that's possible, I tried myself, but didn't acomplish the task.

6th March 2003, 09:46

The borgsoft decoder uses also faad2, but it has it's own format. I didn't play around with that stuff, yet. I made AAC playback work with your direct show filter by doing the following:

wav -> aacenc -> aac -> aac2wav -> wav -> ogmuxer -> ogg

Well, that worked. The file can be played in WMP. I didn't try with video and multichannel yet. I'll give it a go later on. Maybe we can convince syriuc/cyrius (what's his name by the way?) to include support for AAC in ogmuxer or VirtualDubMod? I'll test a little more later on.



P.S.: I found this thread (http://forum.doom9.org/showthread.php?s=&threadid=21926&perpage=20&highlight=AAC%20in%20OGM) , but it seemed to lead nowhere exactly.

6th March 2003, 11:06
Originally posted by tiki4 There we are again: AVI has its problems with VBR audio. Well, that's a known fact. But there is OGM and also Matroska is now at the door.
Sorry to say that AAC is currently not anywhere near the top of our priority list. Once Cyrius would add AAC muxing to VirtualdubMod we were maybe back in bussiness, but there are absolutley no plans for a AAC2matroska.exe or support for AAC in Moritz Bunkus mkvmerger for Linux.

For a better understanding : For every supported codec we have to define exactly how it shall be put into matroska container, means what values are put into the track headers, what data are copied into KaxCodecPrivateDat field, etc. . We just did this for Vorbis and our first test files with XviD and Vorbis play fine in Moritz' mplayer patch, but again, there are no plans for AAC right now. Maybe i am exagerating the problem and its a breeze, because adding AC3 to matroska was done in a day ( we simply put the complete AC3 into matroska, including its own framing, so we can pass it to external decoders for playback ).

Do you think - by any chance - that you find the time to change your DirectShow filter to play AAC from OGM's (or Matroska files)? Until now I wasn't able to mux an AAC into an Ogg container, but I also didn't try to hard. Regards,tiki4

I guess once Nic adapts his filter such that it will play from OGM it should work for matroska also, unless our devs decide to do something fancy and to strip some contents from the AAC streams to cut down overhead a little bit ( doesnt make much sense IMHO ).

6th March 2003, 12:16
Hi Christian,

nice to hear from you again. Actually playing AAC from OGM's is possible. I just didn't try with video yet. But: Muxing is very complicated, because you have to give that thing a WAV header and I think you cannot mux with DirectShow as there is no filter that can read plain AAC files. For me AAC isn't of very high priority at the moment unless there is a filter that can decode 5.1 AAC files. The 3ivx filters for MP4 playback are quite good already but seeking isn't possible at the moment.
For me I'm just playing around with AAC because the sound of that format is quite impressive. Support in Matroska would be nice, but I think you are right to concentrate on the widely adopted formats like Vorbis and AC3.