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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”]
komuta
post Jan 7 2013, 08:57
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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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nu774
post Jan 7 2013, 10:16
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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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Neuron
post Jan 7 2013, 10:32
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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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komuta
post Jan 9 2013, 09:42
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Thanks for both your answers. I'll try this.
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db1989
post Jan 9 2013, 13:11
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Garf
post Jan 9 2013, 17:10
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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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Porcus
post Feb 1 2013, 18:13
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QUOTE (db1989 @ Jan 9 2013, 13:11) *
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