I have tested a lot of programs that use Nero AAC Codec.Most of them have very poor function of the codec settings.As I already wrote a lot of solid LameXP encoder.He knows that is wrong with 5.1 and multi-channel audio. I noticed that mkvtoolnix is because all losses encoders add a small amount of delay of the beginning of the encoded audio.I mainly do mkv movies(x264,AAC)of the middle class so that this lack can usually pass.Of course,I agree with your opinion. Thank you for your comprehensive response I'm fairly sure all of them have the ability to copy the video while converting the audio. Or there's 'one click' type programs such as FormatFactory, AnyVideoConverter, Super etc. I vaguely remember RipBot and HDConvertToX will also copy the video stream, but I'm not 100% sure. Most will only do it the other way around, but there's some which will copy a video stream.

I know when converting with foobar2000 the audio 'padding' is written to the m4a file correctly, although chances are it's actually the Nero encoder which saves that information.Р”Р„lternatively, use a conversion program which lets you copy the video and convert the audio. Then open the MKV with MKVToolnix, deselect the original audio, add the AAC/M4A audio and save it as a new MKV. The first time it'll ask for the location of NeroAAC. Once it's installed you use the convert function, choose AAC (you can setup various presets). It's only a small delay, usually around 50ms, but why not get it correct if you can? Unless conversion programs use the latest MKVToolNix 'behind the scenes' when converting, chances are they don't compensate for the small amount of extra blank audio at the beginning.Р”Р‡oobar2000 is an audio player but it's also a good converter.

MKVToolNix version 5.3.0 onwards takes the 'padding' into account when muxing the AAC audio. In the case of AAC the amount of delay should be written to the m4a file. One reason for using MKVToolNix (at least these days) is because all lossy encoders add a small amount of delay to the beginning of the encoded audio.

Mediahuman audio converter he-aac codec