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constant bitrates, mp4/aac
sd273
post Apr 5 2002, 05:30
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Three questions:

I'm using Psytel Aacenc 2.15.
I tried: aacenc -production -br 256 -low_ath -pns

Why do the demos at http://www.psytel-research.co.yu/showcase.htm have a perfect constant bitrate, ie 192, 128? While my cbr aac files are 252, 251, ect. (aim is 256).

Why do they have the mp4 extension? Whats the difference?

Why do they use mp4_in.dll instead of aac_in.dll in Winamp (i think) and how do i make mine like those with psytel aacenc 2.15? (if i can)

I'm kind of new at this, thanks.
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rjamorim
post Apr 5 2002, 05:58
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QUOTE
Originally posted by sd273
Three questions:

I'm using Psytel Aacenc 2.15.
I tried: aacenc -production -br 256 -low_ath -pns


No, no, no!
You shouldn't use PNS with any bitrate higher than 64kbps. It ruins the quality with anything above that.

QUOTE
Why do the demos at http://www.psytel-research.co.yu/showcase.htm have a perfect constant bitrate, ie 192, 128? While my cbr aac files are 252, 251, ect. (aim is 256).


You should see CBR in psytel as a kind of ABR. I.E: It takes what will be better for each frame around the bitrate you specified.

There are some hidden switches in Psytel to make the files 100% CBR. But they are not mentioned because they tend to degrade quality if used.

QUOTE
Why do they have the mp4 extension? Whats the difference?


They have been wrapped in MP4 container format by a MP4 multiplexer.

It's the same AAC file but inside it's native container. (Not really AAC anymore - I.E: Can't be played/decoded by an ISO AAC-only decoder)

QUOTE
Why do they use mp4_in.dll instead of aac_in.dll in Winamp (i think) and how do i make mine like those with psytel aacenc 2.15? (if i can)


in_mp4 includes, besides faad, the MP4 demultiplexer - so that it first demultiplex the frames, to feed the ISO AAC stream to the FAAD library.

You can wrap AACs in MP4 format with an util find in my programs->Others page - "Set of MPEG4 tools"
I think the program is mp4creator60

QUOTE
I'm kind of new at this, thanks.


No problem. smile.gif

Regards;

Roberto.


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Get up-to-date binaries of Lame, AAC, Vorbis and much more at RareWares:
http://www.rarewares.org
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sd273
post Apr 5 2002, 06:07
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thanks very much for the help
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