Skip to main content

Notice

Please note that most of the software linked on this forum is likely to be safe to use. If you are unsure, feel free to ask in the relevant topics, or send a private message to an administrator or moderator. To help curb the problems of false positives, or in the event that you do find actual malware, you can contribute through the article linked here.
Topic: Can HE-AAC be losslessly transcoded to LC-AAC? (Read 5044 times) previous topic - next topic
0 Members and 1 Guest are viewing this topic.

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 ?

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

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.

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

Reply #3
Thanks for both your answers. I'll try this.

 

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.

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.