Dear friends!

I have several questions about AAC/MP4. Would you please answer the questions as clear as possible? If I'm wrong somewhere - please correct me. I'm sure this discussion maybe useful for many people.
I want to explain to my readers at WebSound.Ru all the nuances of this topic. But in order to perform this I have to understand the things by myself :-)

1. Was .MP4 container standardized?
2. Old .AAC-files streams (except those, that were encoded using Astrid/Quartex & HomeBoy AAC encoders) maybe converted to today's MPEG-4 AAC-streams and then stored in .MP4, isn't it?
2. Which of the software players available today support .MP4? Which AAC profiles they support (Main, LC, LTP, HE-AAC?)
3. Does Apple iPod accept .MP4 files?
4. Is there any difference between .MP4 & .M4A?
5. Which encoders may encode standard .MP4 files? Which profiles they support (Main, LC, LTP, HE-AAC)? What about QuickTime? Sorenson? Nero? FAAC? PsyTel?
6. Is there ANY command line .MP4 encoder available today?
7. Does NEncoder creates standard .MP4 files? Which profile it uses?

Thank you very much in advance
(and sorry for the buggy English)

Yes, it's part of the MPEG4 Systems standard, and is very much based on Apple's MOV container.



I don't understand the question.

And HomeBoy is ISO compliant, Astrid isn't.



Several players. foobar2000, Winamp (w/ plugin), QuickTime, Envivio, Dicas, 3ivX...
All players support LC only, except players based on FAAD2 (Winamp, foobar2000), that support most AAC profiles. 3ivX also supports HE AAC.



Yes



The letter P.



FAAC
NEncode



NEncoder is a frontend for Nero.

3ivx supports all AAC profiles except SSR

modern AAC files contain ADTS bitstreams, and can be remuxed into MP4

older AAC files contain an obselete ADTS bitstream, which can also be remuxed into MP4 with some muxers which support signalling the obselete bitstream

ADIF bitstreams can be converted to ADTS bitstreams, and then remuxed into MP4

I've added parts of this topic to the AAC page at the Wiki so these sorts of quentions don't keep getting asked. I'll browse around the AAC forum some more to find more questions/anwsers to add.

I thought M4A cannot contain videostreams, like MP4. Am I wrong? Isn't it:
MP4: Video, Audio or Both. Intented to be both. Equals the .MPG of MPEG-4.
M4V: Video only. Equals the M1V of MPEG-1.
M4A: Audio only. Equals the MP1, MP2 or most popular MP3 of MPEG-1.

right?

[quote=sinspawn,Feb 1 2004, 03:20 AM] [QUOTE=aradzish,Jan 31 2004, 02:50 PM]
...right? [/quote]
yes and no,


the various extensions are only a help, to use for pure Audio (m4a) foobar and for Video (mp4) mediaplayer classic for example.
But the content is always like mp4.


....cu

Okay.

What about MP3 and MPG then?
Do they have different content?

you have to note that the .m4a extension is purely an invention of apple! it is nowhere mentioned in the mpeg-4 standard!

the mpeg-4 standard defines .mp4 for all sort of content:
audio only
video only
audio + video
audio + video + interactive content
interactive content only
aso...


mp3 is audio only and mpg can carry audio and video

I mean technically. If I rename an mp3 file to mpg, will it play in an mpg-player?.

I don't have any software that doesn't support both extentions, so it's easier to ask you than to bother finding one. I think I remember finding mpg-files containing only audio. Are these really just MP3 files? or MP2 files? Is there an MP1 fileformat?

I'm confused.

.MP3 file is like .AAC file - it's just a pure audio stream without any container format. .MPG files usually contain MPEG Program stream (no necessary though), which can contain video and audio.

-Eugene

Thank you all for this intresting discussion. Now I have several more questions:
1. Please, point me to the best way of encoding of STANDARD .MP4 files which will be playable in the most of available players.
2. if you say that FAAC encodes standard MPEG-4 AAC files, then why these files cannot be opened neither in QuickTime Player nor in Foobar? As I understand the problem is that it produces pure streams? If so, why FAAC doesn't produce .MP4 files? Why the user should pack the streams to .MP4 by himself?
3. Is there any possibility to use Sorenson or QuickTime encoder from the command line?
4. Which type of .MP4 files exactly "understands" iPod? Is the renaming of .MP4 to .M4A works for this purpose?


Sorry for this amount of questions.
I think somebody should create FAQ on this topic. There is a BIG MESS with the files/containers/streams/players. I think, it will be much easier to write such a FAQ once and not to answer these questions each time.
Thank you very much.

AFAIK .m4v is a raw MPEG-4 Video stream, not muxed into mp4 (similar to m1v or m2v), while .m4a is aac muxed into mp4, so it´s not like mp1, mp2 or mp3. .aac is like mp1/mp2/mp3.
So .m4a is only a renamed mp4 with audio only, but .m4v is not a renamed mp4 with video only.