neroAACenc adding audio delay?

[simps]

I just finished reading this...

http://forum.doom9.org/showthread.php?t=156163

Looks like an AAC file encoded with neroAACenc doesn't have the same timecode as the original file.
This means neroAACenc is adding a delay to your audio file and you will get audio/video sync issues.
The delay added by neroAACenc is not big. Looks like it is about 1 frame long or something.
Most people won't notice it, but it is there.

Can someone give us more information about this?
Can it be fixed?

This image shows the sync issue...
http://img259.imageshack.us/img259/5863/compy.jpg

[LoRd_MuldeR]

AAC uses "raw data" blocks with a fixed duration of exactly 1024 samples per block. If the number of samples in your input file isn't a multiple of 1024, then padding needs to happen somewhere...

[simps]

AAC uses "raw data" blocks with a fixed duration of exactly 1024 samples per block. If the number of samples in your input file isn't a multiple of 1024, then padding needs to happen somewhere...

Well, whatever is happening, is happening at the beggining of the file, and that is bad. If it was happening at the end of the file, no audio/video sync would be detectable.

I am doing some research about it, and looks like AAC will add a delay to your audio file, and it is not possible to avoid it. So AAC audio will not be in perfect sync with video. Looks like AC-3 is really a better solution when it comes to audio/video sync. This is sad, looks like AAC is not a perfect solution for audio that has video going with it, because it will never be in perfect sync with the video.

More information here:

http://www.hydrogenaudio.org/forums/index.php?showtopic=67518

Just like LC AAC, HE AAC has a algorithmical delay that cannot be avoided.

[MatLz]

Seems to be a decoder issue.
wav > aac then aac > wav using neroaacenc and neroaacdec is perfectly in sync (at audio frame depth)

[Dark Shikari]

All windowed MDCT formats have a built-in delay, including AC3, MP3, AAC, etc. The decoder is supposed to absorb this delay. If it doesn't, it's broken.

[Zarxrax]

All windowed MDCT formats have a built-in delay, including AC3, MP3, AAC, etc. The decoder is supposed to absorb this delay. If it doesn't, it's broken.

Then just about every decoder out there is broken and we need some serious bug fixing :)

[tebasuna51]

Yes, only NeroAacDec.exe is exact.

All other decoders I test put a delay of 33 ms:

faad command line
bassAudio with MeGUI/BeHappy
DirectShow filters with GraphEdit: ffdshow, ac3fiter, coreaac
DirectShow filter Nero 7 with eac3to

BTW 33 ms is less than a video frame duration and can't be easily noticed.

[simps]

tebasuna51,

Is it 33ms delay for every file, despite its duration?
I really hope this is the case, because it would be even worst if files with longer duration gets larger delays...

[Dark Shikari]

tebasuna51,

Is it 33ms delay for every file, despite its duration?Yes, the delay should be around 1024/(sample rate) seconds.