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Topic: Please, help me understand (Read 3208 times) previous topic - next topic
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Please, help me understand

Hello everybody.

I'm trying to keep myself in sync with today's audio compression technologies, but there are some things I just don't understand. Please, answer me as simple as possible, but also completely, to the following questions:

1. AAC and HE AAC - I understand AAC as another lossy compression format - like MP3, OGG and MPC. What is HE AAC, just a different AAC encoder (like in MP3 we have Lame, Blade and Fraunhoffer for example), or another, not compatible AAC version?

2. What is MP4 - another name for AAC (hoping it will be the next generation MP3) or just a "container" format like WAV, AVI etc?

3. If MP4 is container format, can it contain another stream inside, let's say MP3 or Vorbis, not just AAC stream?

4. MP3 means MPEG 1 Layer 3 - an official standart from Motion Pictures Experts Group. Does MP4 means MPEG 1 (or whatever) Layer 4, or it's just called MP4 because you hope it will be the next generation MP3? Is it official name?

Sorry if you find these questions too simple, but I would like to know more for this promissing new format.

Please, help me understand

Reply #1 –
Quote
1. AAC and HE AAC - I understand AAC as another lossy compression format - like MP3, OGG and MPC. What is HE AAC, just a different AAC encoder (like in MP3 we have Lame, Blade and Fraunhoffer for example), or another, not compatible AAC version?

As far as I know, HE AAC is something like MP3pro. It is in fact AAC with some additional information which tells the decoder how to reconstruct the higher frequencies for lower bitrates.

Quote
2. What is MP4 - another name for AAC (hoping it will be the next generation MP3) or just a "container" format like WAV, AVI etc?

Not sure about this one either, but I think that MP4 uses MPEG 4 while AAC is MPEG 2. Anyway, you might be right about the container idea.

Quote
3. If MP4 is container format, can it contain another stream inside, let's say MP3 or Vorbis, not just AAC stream?

If it is a container format, I am sure that it won't be able to store MP3 or Ogg Vorbis.

Quote
4. MP3 means MPEG 1 Layer 3 - an official standart from Motion Pictures Experts Group. Does MP4 means MPEG 1 (or whatever) Layer 4, or it's just called MP4 because you hope it will be the next generation MP3? Is it official name?

As I said, as far as I know, MP4 is MPEG 4.

Please, help me understand

Reply #2 –
i good way is to search the forum.


1:
AAC is like mp3

then came the SBR tecnolgoy..a way to represtn the hghi freqenc signal by analysing the lwoer spectrum and with som add'ed hitn data.
this is much better then just lowpassing

mp3 + sbr = mp4pros
aac + sbr = HE aac /aac+


2:
mp4 is like avi. only a container it nothing more then a way to collect audio and video into ONE file.
the default audio for mp4 is aac and vqf.


3:
yes i believe so.

4a:
nopes

mp3 = mpeg1/2 layer 3
mp4 = mpeg 4

actually they should have renamed .mp3 to .ml3

4b:
AAC is the next generation of mpeg layer-3.


hope you can use the info
Sven Bent - Denmark

Please, help me understand

Reply #3 –
Thank you, Sven, for your answers, the things are clearer now, but then:

1. In MP3 - it is not sure (yet) that MP3 Pro IS BETTER than MP3 (At least I think so), in AAC, is it KNOWN that HE AAC is better than just AAC?

2. I understand, that MP4 is a container for video & audio. Is it OK to use MP4 for just (AAC) audio stream, or it is better to use AAC file if we use just audio data?

4. MPEG4 - does it mean, that it is a contairner format, officially approved by MPEG? And did THEY said, that is preferable to use AAC stream for audio data in MP4?
Who says that MP4 (read: AAC) IS the next generation MP3? (I'm asking seriously, I am not arguing or so) Are the same big companies behind this standard? What defines it for "the next generation MP3"?

Which AAC encoders are recomended nowadays? Which are highest quality & 100% compatible? As far as I understand, AAC encoders are not free, but I just want to know a little bit more for this format.

Yes, I read the forum completely, and I gather as much information as I can, but sometimes... you know, you have to ask your questions.

Please, help me understand

Reply #4 –
Oops, that was just a repost. Sorry.

Please, help me understand

Reply #5 –
Quote
Thank you, Sven, for your answers, the things are clearer now, but then:

1. In MP3 - it is not sure (yet) that MP3 Pro IS BETTER than MP3 (At least I think so), in AAC, is it KNOWN that HE AAC is better than just AAC?

2. I understand, that MP4 is a container for video & audio. Is it OK to use MP4 for just (AAC) audio stream, or it is better to use AAC file if we use just audio data?

4. MPEG4 - does it mean, that it is a contairner format, officially approved by MPEG? And did THEY said, that is preferable to use AAC stream for audio data in MP4?
Who says that MP4 (read: AAC) IS the next generation MP3? (I'm asking seriously, I am not arguing or so) Are the same big companies behind this standard? What defines it for "the next generation MP3"?

Which AAC encoders are recomended nowadays? Which are highest quality & 100% compatible? As far as I understand, AAC encoders are not free, but I just want to know a little bit more for this format.

Yes, I read the forum completely, and I gather as much information as I can, but sometimes... you know, you have to ask your questions.


answer for 1

No, HE-AAC should only be used for low bitrates, and AAC for higher bitrates.

answer for 2

I would say it is better for use mp4 containing an aac file.  this is because you can optimise it to reduce file size further without any further loss of quality (i think!)

answer for 4

www.audiocoding.com

there was a test done, not to long ago comparing all the aac encoders.  I think QT came on top and nero followed in second place, (but I am not 100% sure on that)
 

Please, help me understand

Reply #6 –
Hi Miles. I also grappled with the same questions you have asked here when I first started getting acquainted with AAC, HE AAC and the MP4 Audio format. I searched the forums here, asked questions and did research to find out about these things. I will do my best to answer your questions:

1. AAC is the replacement for MP3 that was designed by many of the folks who created MP3 (Fraunhoffer and others). HE AAC (High Efficiency AAC) is a new approved extension to the MPEG 4 audio standard that used SBR to enhance the sound at lower bitrates. HE AAC is designed for lower bitrates (under 96k) and AAC LC should be used for better audio quality on bitrates at 96k or above. HE AAC should never be used at higher bitrates. It was designed (like MP3Pro) to enhance the sound of lower bitrate audio only, and never to replace plain standard AAC at higher bitrates. To answer your question, HE AAC is NOT BETTER than AAC, nor is MP3PRO better than MP3. They are a response to make lower bitrates (only) sound better than their native AAC or MP3 counterparts. That's it. I was confused about this also with all the hype around HE AAC and MP3Pro - I thought they were a better sounding format with all the marketing hype they were receiving, but not so.

2. MP4 is a container format approved by MPEG (Motion Pictures Expert Group) that can contain many things, most notably audio and video. MP4 Audio is what we are talking about here, and that includes BOTH AAC and HE AAC in the international standard for MPEG 4 Audio. Use MP4 rather than plain AAC bitstreams. Stick with the MP4 Audio international standard so you file can be played anywhere the NMPEG 4 Audio standard is implemented.

3. Being a container format, by the specifications that have been approved it can include older MPEG 2 and other audio formats, but only those approved by MPEG. So Vorbis is a no go for being inside a MP4 container file. Both AAC and HE AAC are approved to be inside an MPEG 4 contained file. Which one you use depends on your application and the resulting bitrate you desire to use. There is backward compatibility included, but AAC and HE AAC are the "superstars" of the MPEG 4 Audio specification and should be used when making MP4 Audio files.

4. As previously answered by others, MP4 means MPEG 4, while MP3 was "just adopted" to mean MPEG 1 Level 3. Use any encoder you like. Right now there are very few encoders that can produce AAC, HE AAC and both VBR and CBR variants of MP4 Audio files. Nero 6 (www.nero.com) is the most notable one for the PC user. In fact the only reason I purchased Nero 6 was for the MP4 Audio encoding. It still is in its infancy and has some bugs left, but the author (Ivan) is working on fixing any issues. Apple Quicktime scores a bit higher than Nero 6 in listening tests by a small amount. I personally prefer Nero 6 for HE AAC and AAC encoding as it is well supported and updates come out frequently (plus the author, Ivan, is a regular in this forum and is good about responding to bug reports).

Right now Menno has produced a very good WinAmp plugin that plays both AAC and HE AAC files in a .mp4 format well. You can download it from audiocoding.com or rarewares.

I hope these answers help. Welcome to the MP4 Audio world.