Mp4 is a container file type and is used in QuickTime and other apps for storing and playing multi-media data. For more information on MP4 files, see the following URL:
http://www.coolutils.com/Formats/MP4
As I indicated in a previous post, MP4 files that hold audio are identical in every way to M4A files, except for the file extension.
Apple’s documentation suggests that the settings on the Import Settings dialog box are for when you import CDs. They have no effect on files that you buy from the iTunes store. But as I’ll mention further below, these settings do affect the available conversion formats on the context menu for each song in the library.
But these settings do not seem to affect the format of songs that you import into the iTunes library from elsewhere on your hard drive. I just set my import settings to the MP3 encoder, then imported a WAV file. After the import, the WAV file appeared in my iTunes library, still, as a WAV file.
However, when I set my import encoder to MP3, and then examined the context menu for one of my music files, yes indeed, the “Create MP3 version” menu item appeared. So apparently, you have to be configured to import as MP3 in order to see this conversion option on the context menu. This is strange, because in the Preferences dialog box, the Import Settings button is grouped with other options that are specifically importing CDs, including the “When you insert a CD” edit box and the “Automatically retrieve CD track names from the Internet” check box. Further, when you pull up the Import Settings dialog box, it does say that these settings do not apply to selections purchased from the iTuens store. However, it seems to affect the available formats for conversion in the song’s context menu.
It seems counter-intuitive that Import Settings would change the context menu for creating a copy of the song in a different format. After all, the song you’re converting has already been imported into the library; so you’re not really performing an import when you make a differently-formatted version of it.
The layout of the Edit–>Preferences dialog box could be improved by moving the Import Settings button away from the other CD settings, to avoid the misunderstanding that these settings apply to only imports from CDs. Also, it seems that calling these settings “Import Settings” does not totally describe what these settings affect. Instead they might call the button “Import and File Conversion Settings”, or provide two buttons; one called “Import Settings” and the other called “File Conversion Settings”. But software, as well as its accompanying documentation is always imperfect.
Tom Hesley