Losslessly convert AAC file to MP3?

[sldvd]

Is it possible to convert an AAC file losslessly to MP3? Or would doing so necessitate a re-encoding?

Converting it in FFmpeg seems to require a re-encode. Is there any program that can convert AAC to MP3 losslessly?

[jagabo]

Not possible. They are both lossy codecs. Conversion requires decompression and recompression.

[sldvd]

Thank you. In that case, is there any lossless AAC editor for Windows? Looks like there's one for Mac, but I don't know about Windows.

[PuzZLeR]

A good one that I know is GoldWave (not free but worth the small price).

You can just dump any AAC into the interface, (even when it's in an MKV or MP4 file), do your edits, and export as WAV or FLAC if you want lossless.

However, these files will be bigger than your original AAC or the MP3 you wish to target to. If you do wish to make an MP3, it will be lossy at any rate.

[jagabo]

Assuming you mean AAC in and AAC out, losslessly with simple cut/paste editing, I don't know of any audio editor that can do that.

[AlanHK]

Is it possible to convert an AAC file losslessly to MP3? Or would doing so necessitate a re-encoding?

Converting it in FFmpeg seems to require a re-encode. Is there any program that can convert AAC to MP3 losslessly?

As above, impossible, as any conversion into MP3 from another format will involve a loss.

But if you use a high bitrate MP3, say 320 kB, you will be hard pressed to notice the loss.

Note that after doing so you can cut and paste MP3 losslessly using MP3DirectCut.

And also MP3s are limited to two channels only, so if your AAC is multichannel you'll have to downmix.

[PuzZLeR]

Assuming you mean AAC in and AAC out, losslessly with simple cut/paste editing, I don't know of any audio editor that can do that.

The only way I can think of doing this, without loss, in only cutting/joining would be with a "video application" like YAMB, MKVMerge and tsMuxeR in either an MP4 or MKV container (depending).

Not perfect as you may expect - not very frame accurate and lots, and lots, of muxing, demuxing, remuxing...

Since I may only need to do this once a year max I know naught of a better way.

@sldvd: If you want fuller edits than this, such as restoration, dynamics, etc, then I would use Goldwave and the loss would be unavoidable if going to MP3 or back to AAC afterwards. I personally would keep the WAV or FLAC as my Source from then on if such edits were necessary.

[jagabo]

Assuming you mean AAC in and AAC out, losslessly with simple cut/paste editing, I don't know of any audio editor that can do that.

The only way I can think of doing this, without loss, in only cutting/joining would be with a "video application" like YAMB, MKVMerge and tsMuxeR in either an MP4 or MKV container (depending).

Not perfect as you may expect - not very frame accurate and lots, and lots, of muxing, demuxing, remuxing...

Yeah, I was thinking he could mux the AAC audio into a video file. Then use a video editor that doesn't reencode the audio (it doesn't matter if the video gets reencoded -- except for speed), then demux the audio again afterward. That would give accuracy of whatever the frame rate of the video was.

[budwzr]

Why not use the iTunes built in converter and see how it sounds ? The debate of lossless vs. lossy has been going on for decades and surely will continue for eons.

[PuzZLeR]

Yeah, I was thinking he could mux the AAC audio into a video file. Then use a video editor that doesn't reencode the audio (it doesn't matter if the video gets reencoded -- except for speed), then demux the audio again afterward. That would give accuracy of whatever the frame rate of the video was.

Actually, that's an even better idea for "frame accuracy" of the edits (even "frames" is in context here because audio has no "frames").

An AviSynth script could be used, with cuts/joins on an MP4 file, and fed into an encoder as such. Yes, the fastest video encode would apply here since video quality is immaterial.

I know StaxRip used to accept scripts and did audio pass-through (been a while since I had it installed though). I'm sure there are several others that can do this too as well.

Not pretty, but can get the job done until/if a better solution is presented.

(Classic case here of an audio post answered in a "video" forum...)

[jagabo]

I managed to mux an AAC file into a 60 fps AVI video, then trimmed with VirtualDub. One could quickly create a 1000 fps video to get millisecond accuracy if necessary.

[ARTO65]

Whuuuuwhuuu, just found the perfect tool: Free audio dub.
This tool is part of the Dvd video soft "Free studio", but you can download it separately. It's free, but ad supported.
With this tool, I was able to trim a .aac audio file without decompression/recompression.

Not only can you non-destructively trim .aac files, but a whole range of formats.
Free Studio integrates all of the tools of DVD video soft: audio/video converters, downloaders, CD/DVD ripper, burner...
This freeware, and the whole suite is worth a try, there are some very nice tool in there. And yet it's not very well known.

Free audio dub: http://www.dvdvideosoft.com/products/dvd/Free-Audio-Dub.htm
Download page for all the suite and the other tools : http://www.dvdvideosoft.com/free-dvd-video-software-download.htm

Let me know if you give it a try and if it works for you !

[pandy]

Both use MDCT thus at least some "lossless" conversion should be possible. But such software not exist - also i doubt that this software can be created (at least not so easy).

[ARTO65]

Hum... I'm sorry pandy, but what is MDCT ?

[ARTO65]

I spoke too soon. I went to educate myself a little, but I have to admit I didn't precisely understand what MDCT is.
Why do you think this would allow lossless conversion ?

[pandy]

http://en.wikipedia.org/wiki/Modified_discrete_cosine_transform

MP3 and AAC use same transformation (ie MDCT) - in theory conversion between MP3 and AAC in MDCT domain thus "lossless" should be possible - but this is pure academic dispute because no one made such software yet - also i never analyze AAC and MP3 on this how much they have comon in MDCT domain - but unless You use other transformation than native for MP3 and AAC MDCT then You stay on area so called "lossless".

[ARTO65]

Thanks for your reply. I read the wikipedia page, but I have to say I don't understand much of what it says.
Anyway, I guess it would be difficult and not very interesting to develop such software.
Thanks for the imput!