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New MPEG-4 AAC technical corrigendum, With changed ADTS specification....
menno
post Dec 22 2002, 15:59
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Hi,

MPEG put out a new corrigendum to the MPEG-4 stnadard in which they changed the ADTS header format. They actually changed it back to the way it was in MPEG-2 AAC (so no emphasis bits). Since FAAD2 strives to be compliant I will have to make these changes in the decoder, rendering all MPEG-4 AAC ADTS files unreadable.

I will try to write some converting code to solve this problem. This may also be a good reason to start using the MP4 format.

I have no idea why these people decided to change this.

Menno
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Ivan Dimkovic
post Dec 22 2002, 16:15
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I would strongly suggest changing to MP4 file format from old MPEG-4 ADTS files - it offers many advantages over ADTS AAC, and you can always extract AAC tracks for portable devices if necessary.

I think this way of "correcting" things is not fair, because MPEG-4 standard was approved in 1999 and after 3 years they decide to change MPEG-4 ADTS header structure - which was obviously too big thing to be "forgorren" in corrigenda's from 2000 and 2001. But I won't try to speculate and seek other reasons for this sad.gif

Also, at least one encoder I have tested (I won't disclose which) was already "corrected" before this corrigenda was out. So one more reason for changing, though.

This post has been edited by Ivan Dimkovic: Dec 22 2002, 16:16
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ciber-fred
post Dec 27 2002, 10:11
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i menno and ivan ! merry chrismas to all people of this reding board also.

hum.. how could be possible to change a format of a file ? adts is part of aac format no ?
change decoder to decode this new change will be posible if we save decoding of old files...
i won't 'transcode' all my collection of music files to this new aac format... also i could tranlate to mp4
but what about my aac files on cd ?
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menno
post Dec 27 2002, 10:48
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QUOTE (ciber-fred @ Dec 27 2002 - 10:11 AM)
hum.. how could be possible to change a format of a file ? adts is part of aac format no ?

That's easy, make it a standard and after 3 years change the standard sad.gif

QUOTE
change decoder to decode this new change will be posible if we save decoding of old files...
i won't  'transcode' all my collection of music files to this new aac format... also i could tranlate to mp4
but what about my aac files on cd ?


Good question, I have to think about this. It's impossible to detect in the decoder which AAC format is used.

Menno
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menno
post Dec 27 2002, 11:19
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BTW: If you always used the default aacenc.exe you get MPEG-2 AAC files, which are not affected by this change in the format.

Menno
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M
post Dec 27 2002, 11:27
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QUOTE (menno @ Dec 27 2002 - 05:19 AM)
If you always used the default aacenc.exe you get MPEG-2 AAC files, which are not affected by this change in the format.

Hmm... but does this mean that the altered aacenc_mpeg4.exe now produces "useless" results?

- M.
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menno
post Dec 27 2002, 11:55
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Depends on what decoder you use. Current CVS version of FAAD2 will have some problems with these files (will not play them). It's still possible to use mp4creator to change them to mp4 fles.
I've asked for some clarification at the M4IF, but haven't gotten any answer yet. If I don't get a clarification soon, I will start asking/complaining in MPEG itself.

Menno
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hans-jürgen
post Dec 27 2002, 12:15
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QUOTE (M @ Dec 27 2002 - 11:27 AM)
QUOTE (menno @ Dec 27 2002 - 05:19 AM)
If you always used the default aacenc.exe you get MPEG-2 AAC files, which are not affected by this change in the format.

Hmm... but does this mean that the altered aacenc_mpeg4.exe now produces "useless" results?

If I understood Menno right in the "AAC questions..." thread, that's correct. But as it has already been pointed out, you can always convert these AAC files to MP4 files either one by one with in_mp4.dll or in a batch solution with mp4creator and Speek's GUI.

To avoid further confusion it would probably be the best if Roberto took AACENC_MPEG4.EXE away from his website, so that no one can use it anymore for producing non-compatible AAC files in the future.

If there really are some people who encoded and burned non-rewritable CDs with this EXE (and not with the unproblematic AACEnc) , they can always keep an older version of in_mp4.dll that will still play these AAC files from these CDs. But I guess there won't be too many of them anyhow, or am I wrong? wink.gif

This post has been edited by hans-jürgen: Dec 27 2002, 12:32


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Tripwire
post Jan 9 2003, 12:02
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Confusion is good. So when I changed my AAC files to MP4 files with mp4creator, they're fine afterall?
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menno
post Jan 9 2003, 12:04
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Yes, MP4 files are fine.

Menno
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Tripwire
post Jan 9 2003, 12:14
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Thanks. In this case I will continue to use aacenc_mpeg4. Somehow the difference in date between aacenc and aacenc_mpeg4 suggests me somehow that the mpeg4 one has further tuning than the normal one.
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budgie
post Jan 9 2003, 13:24
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Well, that's great, indeed... One of my friends wants all his CD collection (approx. 1400 CDs) have converted into lossy format which would be hardware compatible and of the highest possible quality. I managed him to switch from using MP3 (LAME 3.90.2 --alt-preset insane) into MP4/AAC. But now I'm a bit confused. Would it be without problems? And what encoders to use to avoid incompatibility? He wants his collection to be playable on hardware, which supports AAC and/or MP4. I personally would prefer MP4...
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hans-jürgen
post Jan 10 2003, 00:48
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QUOTE (budgie @ Jan 9 2003 - 01:24 PM)
Well, that's great, indeed... One of my friends wants all his CD collection (approx. 1400 CDs) have converted into lossy format which would be hardware compatible and of the highest possible quality. I managed him to switch from using MP3 (LAME 3.90.2 --alt-preset insane) into MP4/AAC.

If he doesn't care for the extra file size of this LAME setting, he could also go for that, because there are of course much more MP3 hardware players available than AAC at the moment. To use AAC instead only makes sense if he wants to have a high sound quality with smaller files, maybe for a CD portable like Philips Expanium.

QUOTE
But now I'm a bit confused. Would it be without problems? And what encoders to use to avoid incompatibility? He wants his collection to be playable on hardware, which supports AAC and/or MP4. I personally would prefer MP4...


If he only uses PsyTEL AACENC.EXE (without the MPEG-4 appendix), there won't be any problems at all, because this codec produces MPEG-2 AAC files exclusively which can be played back on a compatible hardware player. Nero AAC can do the same, if he enables the "ISO bla....." option which also puts out MPEG-2 AAC files.

At the moment there aren't any hardware players that can play *.mp4 audio files, as far as I know, so there's no reason to convert or produce them yet considering the hardware support. When those players will arrive some time, there's always the possibility to convert all existing AAC files to MP4 with mp4creator, even if they were written onto a non-rewritable CD (write the converted MP4 files from the CD to your HDD then).


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budgie
post Jan 10 2003, 10:00
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hans-jürgen:

Thanx!
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