Difference between AAC (lav) and AAC (Fraunhofer) audio codec?

[pxstein]

In most of the video converters users can choose between two AAC codecs/encoders:
- (default) AAC (lav)
and
- Fraunhofer AAC

Is there a significant difference between them?

In particular I am interested if there is a negative impact on (later) keyframe-oriented cutting and on audio-video syncing

[hello_hello]

I'm guessing, but I think AAC (lav) is probably the native ffmpeg encoder. Of the freely available encoders, it's probably the lowest quality, although they're all quite good at decent bitrates.
Fraunhofer AAC is probably the encoder supplied with the last version of WinAMP. It should be quite good.

QAAC is considered to be one of the best, if not the best, AAC encoder. It uses the Apple itunes encoder. If you have itunes installed you can download and run QAAC. If you don't, you can download the full/offline itunes installer and extract the necessary files. There's no need to install itunes.

All lossy encoders use frames, so the audio has to be cut on an audio frame, but any decent muxing program would add an appropriate audio delay after removing an audio frame when cutting, assuming it's necessary. The length of an audio frame is quite small.
Lossy encoders also add padding to the beginning and end of the audio. Usually for AAC, information is saved to the MP4/M4A container so players can skip the padding (gapless playback). If that information is present, MKVToolNix will use it to remove the padding and/or automatically apply an audio delay to compensate so the AV sync remains exact.

QAAC is the only encoder (as far as I know) with an option to not pad the beginning of the audio with silence. The command line argument is --no-delay.

Here's a link for a version of foobar2000 I uploaded a while back.
foobar2000 portable (for audio encoding)
It's a portable version so you can just unzip and run it. It's ready to go for encoding with the freely available AAC encoders, and it comes with conversion and encoder presets for converting just about any format to any format. About the only thing you need to do is download and put ffmpeg in the encoders folder for decoding/encoding some audio types. The necessary files for encoding with QAAC are included. There's also conversion and DSP presets for downmixing and/or compression. It's a year or so old now, but everything runs on XP.

Some links
QAAC
I think the current makeportable2.cmd file for extracting the required files from the itunes installer is here, if you want to update the encoder to the latest version, or the 64 bit version, at some stage.

[pxstein]

So Fraunhofer AAC is better than AAC (lav)?
and should be used if available?

Is there any disadvantage for Fraunhofer AAC (e.g. when cutting and/or editing audio)?

Can I use both in MP4 video containers together with H.264 video codecs?

[jagabo]

Is there any disadvantage for Fraunhofer AAC?

If Fraunhofer finds you using their encoder without a license they may sue you.