No. Although XMF and XML are both extensible, XMF avoids XML technology in order to minimize overhead, data size, and code size.
Just get the XMF Specification documents and start implementing.
No. XMF is freely usable. The only thing you have to pay for is buying the specification documents.
No, but you will probably need to obtain the specification documents from the MMA.
XMF is a technology for wrapping collections of other music and sound resource types, such as MIDI files and DLS and digital audio files. XMF itself does not describe musical notes, notation, instrument sounds, or audio recordings. Instead, it gives content creators a way to pull all those elements together into a single file, for easier handling and more consistent, predictable playback.
The XMF container format allows a collection to include files on remote web servers, via URL, just as easily as including data directly in the XMF file. Flexible data compression is also built directly into the container, for faster file downloads.
There are several different types of XMF file, and the answer to this question depends on which type you mean.
The most popular use of XMF is currently for mobile phone content, via the Mobile XMF file type. Many mobile phones can already open and play Mobile XMF files; check your phone's documentation. See our XMF Products page for a partial list of Mobile XMF file authoring tools.
XMF music/sound player software for other music composition applications should also appear shortly. If developers will let us know about them, we'll post the information on our XMF Products page.
You can arrange the resources in an XMF file in any hierarchy you prefer, like the folders and files in a file system. You can add custom resource types to an XMF file very easily, and any other application that opens the file will ignore them. You can also add custom Meta-Data items to any resource, and control whether other applications will be able to read and display it. You can apply your own data-compression or encryption system at the individual resource level (although other applications will not be able to read those packed resources). Extensions that prove generally useful can be incorporated into the public XMF standard at any point, if you wish.
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