[Default parameters] MP4 conversion not allowed for AAC audio
By default, if we want to convert a video to produce an HTML5 compliant MP4 video, we have to modify default parameters: default audio is mp3, and norm usually plans to use AAC. But it is not enough: in this case, to avoid an error message, it is mandatory to modify the "strict standard respect" to "-2".
I think, as HTML5 is a huge standard now, we should be able to produce mp4 [H264+AAC] files with an easy way, without be looking for this "-2" trick.