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Topic: Can HE-AAC be losslessly transcoded to LC-AAC? (Read 3129 times) previous topic - next topic

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  • komuta
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Can HE-AAC be losslessly transcoded to LC-AAC?
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 ?

  • nu774
  • [*][*][*][*][*]
  • Developer
Can HE-AAC be losslessly transcoded to LC-AAC?
Reply #1
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: [Select]
mp4box -raw input.m4a && mp4box -add input_track1.aac -new output.m4a

  • Neuron
  • [*][*][*]
Can HE-AAC be losslessly transcoded to LC-AAC?
Reply #2
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: [Select]
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.

  • komuta
  • [*]
Can HE-AAC be losslessly transcoded to LC-AAC?
Reply #3
Thanks for both your answers. I'll try this.

  • db1989
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  • Global Moderator
Can HE-AAC be losslessly transcoded to LC-AAC?
Reply #4
I knew I should never have changed my avatar away from a red panda; now I’ve been usurped.

  • Garf
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  • Developer (Donating)
Can HE-AAC be losslessly transcoded to LC-AAC?
Reply #5
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.
  • Last Edit: 09 January, 2013, 11:11:07 AM by Garf

  • Porcus
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Can HE-AAC be losslessly transcoded to LC-AAC?
Reply #6
I knew I should never have changed my avatar away from a red panda; now I’ve been usurped.



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