Can HE-AAC be losslessly transcoded to LC-AAC?, [TOS #6: moved from General Audio, was “HE-AAC to AAC transcode”] |
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Can HE-AAC be losslessly transcoded to LC-AAC?, [TOS #6: moved from General Audio, was “HE-AAC to AAC transcode”] |
 Jan 7 2013, 08:57
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#1
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 Group: Members Posts: 2 Joined: 7-January 13 Member No.: 105660  |
Hi,
I was wondering if it was possible to transcode losslessly from HE-AAC to AAC. I have a peace of HE-AAC audio which I would like to listen to on a HE-AAC incompatible hardware. My understanding of HE-AAC being it's roughly AAC LC with SBR to gain over bitrate, I thought it might be possible to reconstruct the 48KHz symmetric AAC frame without loss. Would anyone here know if it is possible ? |
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Jan 7 2013, 10:16
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#2
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 Group: Developer Posts: 295 Joined: 22-November 10 From: Japan Member No.: 85902 |
I think it's likely that your hardware can play HE-AAC file as LC-AAC if it is implicitly signaled.
If your hardware supports ADTS playback, try it first. If not, try remuxing like the following: CODE mp4box -raw input.m4a && mp4box -add input_track1.aac -new output.m4a
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Jan 7 2013, 10:32
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#3
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Group: Members Posts: 84 Joined: 14-December 12 Member No.: 105171 |
QUOTE (nu774 @ Jan 7 2013, 10:16)  I think it's likely that your hardware can play HE-AAC file as LC-AAC if it is implicitly signaled. If your hardware supports ADTS playback, try it first. If not, try remuxing like the following: CODE mp4box -raw input.m4a && mp4box -add input_track1.aac -new output.m4a AFAIK HE-AAC plays the LC-AAC part on HE incompatible software/hardware. The sample rate will probably only be 22 Khz through. |
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Jan 9 2013, 09:42
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#4
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Group: Members Posts: 2 Joined: 7-January 13 Member No.: 105660 |
Thanks for both your answers. I'll try this.
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Jan 9 2013, 13:11
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#5
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Group: Super Moderator Posts: 4352 Joined: 23-June 06 Member No.: 32180 |
I knew I should never have changed my avatar away from a red panda; now I’ve been usurped.
 
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Jan 9 2013, 17:10
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#6
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 Server Admin Group: Admin Posts: 4808 Joined: 24-September 01 Member No.: 13 |
HE-AAC consists of a 22kHz LC-AAC file, with some extra info (the HE part) on how to best guess the upper 22kHz from the LC part.
Non-HE-AAC players will see and play the 22kHz LC-AAC part and simply not do the extra reconstruction. "Lossless transcoding" is a bit of a strange concept in there. |
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Feb 1 2013, 18:13
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#7
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 Group: Members Posts: 1471 Joined: 30-November 06 Member No.: 38207 |
QUOTE (db1989 @ Jan 9 2013, 13:11) I knew I should never have changed my avatar away from a red panda; now I’ve been usurped. You reap what you ...   -------------------- geocities.com/hydrogenaudio: http://goo.gl/tqYZj
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Lo-Fi Version | Time is now: 24th May 2013 - 11:19 |
